Falcon Heavy Static Fire

In article ,
says...

On 2018-01-28 20:48, Jeff Findley wrote:

Yes. Falcon 9 is about as tall as it can be for its width. This does
not change for Heavy, so they're simply reusing the upper stage pretty
much as-is.

Does this mean that "in production", the stage 2 for a Falcon Heavy
couldn't have that much more fuel than as currently designed for Falcon 9?

I was thinking that more fuel for Stage 2 could be a part of the
"heavier payload" that stage one can lift and that Stage 2 could then
get the actual payload out higher and faster.

There really isn't room unless they made the upper stage wider. And you
can see from pictures it's no taller (it can't be, as I already
explained).

I'm not sure what you mean by "into Sun".

Meant into a solar orbit sorry. Do you know how this will be done?


Will Stage 2 spend a few orbits around earth before reaching escape
velocity? Or will Stage 2 continue in same path as Stage 1 left it and
reach escape velocity before having completed 1 orbit ?

Entering earth orbit would be pointless on a flight without a crew. It
would also be a waste of fuel/oxidizer, so I seriously doubt they'd do
that.

They only did it on Apollo to double check some things before performing
TLI (i.e. safety reasons). It wasn't the most optimal way to get to the
moon though.

Or is launch timed and oriented such that it will be all done in one
shot, with stage 2 starting its engines as soon as separate from stage 1
and reaching escape velocity within say half an orbit ?

The latter. Lingering doesn't do anything but use up some of the
limited (battery and LOX boil off) lifetime of the upper stage.

snip - I think the above is sufficient.

My guess is they
won't even bother to separate the car from the upper stage so the car
will be easier to track.

Will Stage 2 deploy solar array or have some RTG battery so it remains
"alive" for a long time to keep comms with Earth ? or will it become
totally dead/inert and be garbage in the sky ?

No solar arrays, no RTG. SpaceX released high resolution pictures of
the car on top of the payload adapter with the payload fairing pieces in
the background. There are pictures from all four directions around the
car. There are no solar arrays or RTG radiators visible in any of the
pictures. RTG is laughable (you can't exactly buy one from Amazon.com).

Determining the exact (solar) orbital
parameters will verify the performance of Falcon Heavy.

Won't finding out the parameters of Stage 1 at time of separation be the
more determining (and accurate) factor of its performance?

That tells you nothing of second stage performance. If all they wanted
was performance of the boosters and core, they'd have put a dummy upper
stage on top. They didn't. Surely they'll want to measure the final
orbital parameters of the combined upper stage and dummy payload.

If this were a LEO payload at the heaviest end of what Heavy can lift,
then the boosters would stage at a much lower altitude and speed than on
this test flight.

Which means the vehicle would have to be capable of operating under very
different scenarios.

As do the ULA EELVs. Do note that launching a relatively light "deep
space probe" at a very high velocity is a bit different than launching a
very heavy optical spy satellite into a relatively low earth orbit.
Both trajectories are well within what any EELV class launcher can do.
Falcon Heavy will be qualified to launch "heavy" EELV payloads (standard
payload adapter, and etc).

For the Shuttle, was there much variation in altitude/speed where SRBs
separated based on Shuttle's cargo? (or after it was made lighter with
major maintenance and ET overhaul etc) ?

Google broken? SSME's got tweaked a bit but more or less remained the
same from a performance perspective. Orbiters later than Columbia were
built a tad bit lighter, but in the overall scheme of things that wasn't
very much mass saved. The advanced filament wound boosters were
canceled due to high cost, so no joy there. The only real performance
upgrades worth a damn were the lightweight ET (done fairly early on
based on flight test data) and for ISS the super lightweight ET (which
used a lighter weight aluminum-lithium alloy instead of the original
aluminum alloy).

Hopefully, but parallel staging is still a huge risk. You don't want
the boosters to get "hung up" or to "recontact" the core in any way.

If, at the altitude they separate, it is essentially vaccum, doesn't
that make it much easier to avoid recontact?

Easier. But easier still isn't a sure thing. There really is no
perfect substitute for flight testing in a scenario like this. You
simply can't test this on the ground. You run your simulations and you
fly a test flight.

I wonder how the radios will work. When going up together, will boosters
be "slaves" to the central core control system, but once thet separate,
they establish radio contact and become independant to get back to
earth? Or would each have independnt links to ground trhougout the
flight and just share the data amongst themselves during the attached
portion of flight?

NASA didn't take any chances with the shuttle SRBs. They had
multiply
redundant separation motors at both the nose and on the aft skirt to
insure a "clean" separation.

But the SRB's engines didn't have a clean "ON/OFF" switch for their engines.

By clean separation I meant not getting "hung up" on the rest of the
stack and not "recontacting" the rest of the stack. The method of
separation doesn't really matter as long as those criteria are met.

Will be interesting to see if SpaceX explains this on launch day. They
probably don't want to jettison "dead weight" and would prefer boosters
still generating at least equal lift, but on the other hand, they don't
want that exhaust to go and burn the core stage either.

They will almost certainly use the reaction control system (small liquid
fueled rocket engines) on the boosters to aid in a clean separation.
These are the same tiny engines that are used on a normal flight to
maintain attitude control in vacuum. You can't land a Falcon 9 first
stage without them, so they have much experience with them and what they
can and cannot do.

Yes, it will surely reserve more fuel for the reentry burn compared to a
"normal" Falcon 9 reentry burn. But, since it will be landing on the
barge, it won't need a "boost back" burn, so that ought to balance
things out a bit.

Will the barge still be relatively close to KSC or would it be closer to
Africa because core stage expected to travel much further downrange?
(with a ballistic descent, much of forward speed can be bled in
atmosphere, no need to "brake and reverve direction".

Google it. Look for the exclusion zones for boats and aircraft. The
big rectangle out in the Atlantic east of KSC is the exclusion zone for
the core (first) stage. Then compare that zone to all of the different
zones for Falcon 9 launches. There's your answer.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.

JF Mezei wrote:

On 2018-01-28 08:44, Jeff Findley wrote:
In article ,
says...

Musk just Tweeted that they are aiming for Feb 6 launch for Falcon Heavy

I saw that last night. So only a bit more than a week away. Exciting
times.


Would it be fair to state that in terms of "spectacular"
rocket-goes-kablooie" during launch and near the pad, majority would be
the engine turbines that go amok and break apart causing a great big
ball of fire ?


No. Much more likely is that simultaneous ignition of all engines
fails and this stresses the connections between the cores to the point
where the booster breaks up.


Considering the Merlin engines have been tested quite a bit, shouldn't
there be a good confidence level and Musk's "it will likely fail" is
just PR stunt to make the lanch more "interesting" ?


No. He's just 'managing expectations' on a very challenging initial
launch. I'm sure that SpaceX is much more interested in data they'll
collect during the flight than they are in getting a Tesla roadster to
Mars orbit.


Space X web site shows that the stage 2 for Falcon Heavy will be
identical to Stage 2 from Falcon 9 (397s of burn time, 934kN thrust).

So if Falcon Heavy is able to throw a car out of Earth orbit into Sun,
something Falcon 9 can't do, it would mean that Falcon Heavy will be
dropping stage2 and the car at higher orbit/velocity, right ?


Who said anything about putting a car out of Earth orbit into the Sun?
Here's a hint. Falcon 9 FT can put around 4 MT into TMI. That's
easily a car to Mars. Falcon Heavy can put 16.8 MT into TMI.


Falcon 9 Stage 1 burns for ~160 seconds. Will the side boosters on
Falcon Heabvy burn for same amount of time and detach at roughly same
altitude/speed as Falcon 9 (somewhere between 80 and 100km altitude) ?


I would expect the separation TIME to be the same, since the side
boosters burn at 100% from launch to burnout. The difference, of
course, is that once the side boosters separate a Falcon Heavy still
has a big chunk of a Falcon 9 core performance left, since the center
core throttles back until separation of the side boosters.


If so, correct to state that this operation will occur in much thinner
almosphere than the Shuttle SRB separation and this far less aerodynamic
challenges?


Yes, the separation will be higher than Shuttle SRBs. However, your
conclusion doesn't follow, since the concern is Q rather than just air
density and Q is affected by velocity. Falcon Heavy separation will
be higher than Shuttle SRB separation, but will occur at higher
velocity.


Since the core stage will throttle down early on which will allow it to
continue to push the stack after the boosters have left, it also means
that it will be dropping its payload at far higher and faster (and more
distance from launch site) than a Falcon 9 would have.


Only for identical payloads. What you really buy is more payload to
the same place. If you don't need the extra payload capability you
just shut the stage down early.


Does this imply that the core stage will have to keep a lot more reserve
fuel to "brake" to drop out of the sky? Would the barge be located
signifancly more downrange from the pad so that the core stage wouldn't
have to travel as much on its return trajectory?


No.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn

In article ,
says...

JF Mezei wrote:

On 2018-01-28 08:44, Jeff Findley wrote:
In article ,
says...

Musk just Tweeted that they are aiming for Feb 6 launch for Falcon Heavy

I saw that last night. So only a bit more than a week away. Exciting
times.


Would it be fair to state that in terms of "spectacular"
rocket-goes-kablooie" during launch and near the pad, majority would be
the engine turbines that go amok and break apart causing a great big
ball of fire ?


No. Much more likely is that simultaneous ignition of all engines
fails and this stresses the connections between the cores to the point
where the booster breaks up.

The Falcon Heavy hot fire test already happened and was successful, so I
personally think that's unlikely to happen. Also, from what I've read,
ignition of the Merlin engines does not occur simultaneously on Falcon
Heavy. On Heavy, they've decided to start the engines with a very small
delay between them. From what I understand, the space shuttle did the
same with the SSMEs. It's just that the delay is so small, it looks
simultaneous unless it's filmed with a high speed camera and you slow
down playback.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.

In article ,
says...

On 2018-01-29 06:21, Jeff Findley wrote:

Entering earth orbit would be pointless on a flight without a crew.

I was thinking more in terms of going around until it is aligned to the
path to escape Earth and become in orbit around the sun. (aka: liberal
launch window because you adjust when you start the escape engine burn).

You can also do that by carefully choosing the time of the launch.
We'll see on launch day, won't we? SpaceX usually does a good job with
their live coverage (of non-classified) missions.

would also be a waste of fuel/oxidizer, so I seriously doubt they'd do
that.

In what way would it be a waste? Because it might slow down at perigee
due to some thin atmosphere?

That and if you're aiming for an escape trajectory, you don't care how
low "perigee" is, because you're never going to experience it. So why
waste fuel on raising it about the ground at all?

The latter. Lingering doesn't do anything but use up some of the
limited (battery and LOX boil off) lifetime of the upper stage.

Fair enough. But...

Earth is ~150 million km orbit, Mars is ~228 million km. Or roughly 78
million km difference in diametre.

If Stage 2 only has "hours" autonomy on batteries, how does it expect to
not onlu escape Earth's travity, but also increase its orbit around the
sun by som 78 million km and circularize it?

It's not going to be in a circular orbit. It's going to be in a Hohmann
transfer orbit between earth's orbit and Mars' orbit. It's just that
Mars won't be there when it gets there. Presumably earth won't be there
either

With all the fancy orbital mechanic tricks, doesn'it need at least a
quarter orbit around the sun to get into mostly circular orbit? (which
would be 171 days. (Mars tear is 687). Seems to me that spending an
extra 900 minutes for 1 spin around the Earth shouldn't be a big deal in
terms of autonomy.

No, as long as you escape earth's orbit, you're in a solar orbit.
SpaceX doesn't care if it's circular, why would they? They're
simulating a Mars mission, without entering Mars orbit. Again Hohmann
transfer orbit between earth orbit and Mars orbit.

That tells you nothing of second stage performance. If all they wanted
was performance of the boosters and core, they'd have put a dummy upper
stage on top. They didn't. Surely they'll want to measure the final
orbital parameters of the combined upper stage and dummy payload.

Since second stage is allegedly identical to that of Falcon 9, don't
they already have full performance data on it?

Not in this configuration.

From engine performance point of view, is there much difference in
"vacuum" between where Falcon 9 normally delivers stage2 and where
Falcom Heavy will deliver it ?

USAF is certifying Falcon Heavy for launches, so they want to test the
entire system "end to end".

As do the ULA EELVs.

But EELVs don't land back at a designated spot. So the big diffrerences
in what Falcon Heavy can do (high/fast for light loads) or low/slow for
heavy loads) would result in very different parameters for the stages to
re-enter and land.

USAF doesn't much care about landings, unless it screws up their launch.
So SpaceX wants to test the entire system "end to end", including
landings so that the USAF will have confidence in the entire system,
including landings.

Google broken? SSME's got tweaked a bit but more or less remained the
same from a performance perspective. Orbiters later than Columbia were
built a tad bit lighter, but in the overall scheme of things that wasn't
very much mass saved.

Wasn't there much weight saved when top skin was changed from tiles to
blankets? Wight saved when buil-in airlock removed ? glass cockpit
upgrades and many structural changes and some insyrumentation removed in
the structure ?

A tiny amount in all those cases, except "structural changes". That's
why Columbia is heavier. It was the first space-worthy orbiter, so
didn't get the full benefit of the structural weight reduction program.

Also, didn't SSMEs get performance upgrades of somewhere around 5% since
they would go to 105% of rated performance during launch ?

Yep, another small amount there as well. The program was pretty
desperate to reduce mass on the orbiter and the ET. They were scrubbing
mass from the most insignificant of things to save a kg or two here and
there.

As far as I know, the program never quite met it's original payload
goals (as set by the USAF). Doubly true with Columbia. It was the
"heavy" orbiter and was relegated to missions that were on the low end
of the performance spectrum.

Easier. But easier still isn't a sure thing. There really is no
perfect substitute for flight testing in a scenario like this. You
simply can't test this on the ground. You run your simulations and you
fly a test flight.

At altiutude boosters are expected to pop out, is atmosphere/drag a
consideration for the few moments where there is danger? Or Is this
basically a newtonian process of pusging the boosters out gently and
they continue to gently move away as core accelerates ahead ?

It depends on Q, which is the dynamic pressure experienced at the speed
and altitude that the boosters drop off. It'll be higher than SRB sep
on the shuttle, but will surely be faster as well.

Dynamic Pressure
https://www.grc.nasa.gov/www/k-12/ai.../dynpress.html

See that squared term on velocity in the dynamic pressure equation? The
devil is in the details here. We'll know more come launch day when the
live feed will show altitude and velocity at booster separation. Then
you can "plug and chug" to get Q.

I guess the one big variable is that since the boosters are not
expandable, it isn't just ensuring they don't cause damage to core
stage, but also that the core stage's engines don't burn the boosters as
it accelerates ahead of them.

Well, yeah, if you want to reuse them that's a consideration, isn't it?

I wonder what sort of video feeds we'll have of that operation.

Falcon 9 typically has at least one rear facing camera on the
"interstage" section of the first stage. I'd imagine for Heavy, they'll
have at least one camera on the "interstage" for each booster (maybe
more for redundancy). The engineers are going to want data on the
separation. Cameras are a great way to get some of that data.

Google it. Look for the exclusion zones for boats and aircraft.

I googled exclusion zone atlantic falcon and it gave me unexpected
results... some footbal team :-)

OK, so he core still lands well inside the US territorial waters. Does
this mean that it kills forwards velocioty and starts to travel back to
KSC on its way down like Falcon 9s ? Or could this distance still allow
a ballistic of rapid up, drop stage 2, and rapid down, always with
eastbound horizontal speed ?

Sorry, I don't have time to look this up. I need to get to work on
time. I did see a pic on Twitter, surely taken from whatever US
Government website issues warnings to ships and the like. The
information is out there, you just have to look for it.

Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.

Jeff Findley wrote:

In article ,
says...

JF Mezei wrote:

On 2018-01-28 08:44, Jeff Findley wrote:
In article ,
says...

Musk just Tweeted that they are aiming for Feb 6 launch for Falcon Heavy

I saw that last night. So only a bit more than a week away. Exciting
times.


Would it be fair to state that in terms of "spectacular"
rocket-goes-kablooie" during launch and near the pad, majority would be
the engine turbines that go amok and break apart causing a great big
ball of fire ?


No. Much more likely is that simultaneous ignition of all engines
fails and this stresses the connections between the cores to the point
where the booster breaks up.


The Falcon Heavy hot fire test already happened and was successful, so I
personally think that's unlikely to happen.


True, but it's probably still the most likely 'dramatic' failure close
to the pad.


Also, from what I've read,
ignition of the Merlin engines does not occur simultaneously on Falcon
Heavy.


It certainly didn't during the hot fire test. There was significant
time (seconds) between core starts.


--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw

JF Mezei wrote:

On 2018-01-29 06:21, Jeff Findley wrote:

Entering earth orbit would be pointless on a flight without a crew.

I was thinking more in terms of going around until it is aligned to the
path to escape Earth and become in orbit around the sun. (aka: liberal
launch window because you adjust when you start the escape engine burn).


Just use a reasonable launch window and that's not necessary.


would also be a waste of fuel/oxidizer, so I seriously doubt they'd do
that.

In what way would it be a waste? Because it might slow down at perigee
due to some thin atmosphere?


Because you have to do a high burn to get an orbit that you wouldn't
need to do if you go directly to a transfer path.


The latter. Lingering doesn't do anything but use up some of the
limited (battery and LOX boil off) lifetime of the upper stage.

Fair enough. But...

Earth is ~150 million km orbit, Mars is ~228 million km. Or roughly 78
million km difference in diametre.

If Stage 2 only has "hours" autonomy on batteries, how does it expect to
not onlu escape Earth's travity, but also increase its orbit around the
sun by som 78 million km and circularize it?

With all the fancy orbital mechanic tricks, doesn'it need at least a
quarter orbit around the sun to get into mostly circular orbit? (which
would be 171 days. (Mars tear is 687). Seems to me that spending an
extra 900 minutes for 1 spin around the Earth shouldn't be a big deal in
terms of autonomy.


Since they're just going out to Mars orbit (in a transfer ellipse) and
not actually going anywhere near Mars, why would they get any kind of
'circular orbit'.



That tells you nothing of second stage performance. If all they wanted
was performance of the boosters and core, they'd have put a dummy upper
stage on top. They didn't. Surely they'll want to measure the final
orbital parameters of the combined upper stage and dummy payload.


Since second stage is allegedly identical to that of Falcon 9, don't
they already have full performance data on it?


But they don't have any data on its performance starting from where a
Falcon Heavy launch leaves it.


From engine performance point of view, is there much difference in
"vacuum" between where Falcon 9 normally delivers stage2 and where
Falcom Heavy will deliver it ?


Depends on a lot of things. There certainly could be.


As do the ULA EELVs.

But EELVs don't land back at a designated spot. So the big diffrerences
in what Falcon Heavy can do (high/fast for light loads) or low/slow for
heavy loads) would result in very different parameters for the stages to
re-enter and land.


Would it? Returning stages hit terminal velocity due to air drag on
the way down, regardless of how 'fast' and 'high' they start from.

snip remaining bootless speculation


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn

JF Mezei wrote:

On 2018-01-30 06:09, Jeff Findley wrote:

That and if you're aiming for an escape trajectory, you don't care how
low "perigee" is, because you're never going to experience it. So why
waste fuel on raising it about the ground at all?

Side question:

If you are in orbit for a few hours and then leave to Jupiter and
beyond. Does spending fuel to circularize that orbit at apogee for those
few hours end up reducing fuel needed once you fire engines to get to
espape velocity?


No. In fact, it's usually the reverse.


Since a craft in circular orbit at altitude X has more energy than same
craft at elliptical orbit with apogee at X, I am wondering if that extra
energy offers *any* help when leaving to escape Earth.


Your premise is faulty and poorly thought out. And the answer is
essentially 'no'.


It's not going to be in a circular orbit. It's going to be in a Hohmann
transfer orbit between earth's orbit and Mars' orbit. It's just that
Mars won't be there when it gets there. Presumably earth won't be there
either

Hohmann, from what that Internet thing tells me is to transfer from one
circular to another circular orbit and requires a burn once you reach
the destination altitude to "stay there".


Correct. This is the difference between TMI and Mars orbit.


If the Tesla is going to be in elliptical orbit with perigee at Earth
and Apogee at Mars altitudes, doesn't that have a risk that it will come
back to Earth at some point ?


Odds are tiny and it's easily prevented.


(this is in a context of battery autonomy and ability to fire engines
much later to at least raise perigee to above earth's orbit around sun)


simulating a Mars mission, without entering Mars orbit. Again Hohmann
transfer orbit between earth orbit and Mars orbit.

I was confused by reading that they would send the Tesla into an orbit
around the sun matching Mars. (as opposed to stating it was a highly
elliptical orbit around the sun between Earth and Mars altitudes).


They didn't say that. Hence your confusion.


Since second stage is allegedly identical to that of Falcon 9, don't
they already have full performance data on it?

Not in this configuration.

So what is different in terms of Stage 2's performance if the hardware
is identical?


What is the difference in terms of your car's performance in
accelerationg from 30 MPH on a road 2,000 feet MSL and accelerating
from 50 MPH on a road 5,000 feet MSL if the hardware is identical?

snip usual Mayfly Mauling a Mortified Mare


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn

JF Mezei wrote:

On 2018-01-30 08:12, Fred J. McCall wrote:

Would it? Returning stages hit terminal velocity due to air drag on
the way down, regardless of how 'fast' and 'high' they start from.


Re-usable stages, compared to EELVs, need to consider heat of re-entry,
keeping enough fuel to return to land, and attitude control with
thrusters and then aerodynamic devices. So there are plenty of
differences when a stage goes up much higher and farther and needs to
return to land compared to expandable stages who want to burn up on
re-entry.



You think so, do you? Do the math.


--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn

In article ,
says...

On 2018-01-30 06:09, Jeff Findley wrote:

That and if you're aiming for an escape trajectory, you don't care how
low "perigee" is, because you're never going to experience it. So why
waste fuel on raising it about the ground at all?

Side question:

If you are in orbit for a few hours and then leave to Jupiter and
beyond. Does spending fuel to circularize that orbit at apogee for those
few hours end up reducing fuel needed once you fire engines to get to
espape velocity?

No. That's why I said in a previous post it is a waste to do so if your
goal is to get past earth escape velocity. I took a 500 level orbital
mechanics class when I was at Purdue. It was surely the 2nd hardest
class I ever took. Professor Howell, who taught the class, came to
Purdue from JPL where she used to simulate trajectories of planetary
missions, including planetary fly-bys. I remember a few things from
that class.

It's not going to be in a circular orbit. It's going to be in a
Hohmann
transfer orbit between earth's orbit and Mars' orbit. It's just that
Mars won't be there when it gets there. Presumably earth won't be there
either

Hohmann, from what that Internet thing tells me is to transfer from one
circular to another circular orbit and requires a burn once you reach
the destination altitude to "stay there".

I said it's going into a Hohmann transfer orbit. Then it's done because
no more battery power and no more fuel in the Falcon upper stage. The
upper stage with the car attached will stay in that Hohmann transfer
orbit, continuously cycle between earth's orbit and Mars' orbit, until
something else perturbs its orbit. My guess is that it will eventually
be perturbed by either earth or Mars and then who knows what it's going
to do because it will depend on the exact details of the interaction.
Again, orbital mechanics is not easy.

If the Tesla is going to be in elliptical orbit with perigee at Earth
and Apogee at Mars altitudes, doesn't that have a risk that it will come
back to Earth at some point ?

If it is possible depends on the details of the final orbit. Again,
we'll have to wait until it's in that orbit to predict what might
happen.

If this happens it will almost surely burn up on reentry. **** falls to
earth all the time. It's not like this thing is huge like Skylab.

(this is in a context of battery autonomy and ability to fire engines
much later to at least raise perigee to above earth's orbit around sun)

Batteries will be dead long before that. And any LOX in the oxidizer
tank will have boiled off completely as well. You're not going to do
anything with a dead battery and only kerosene fumes in the fuel tank.

I don't know how to put this any more clearly. There will never be a
circularization burn at Mars' orbital distance. There simply can't be.
it's just not physically possible using the stock Falcon upper stage
with Merlin engine.

Since second stage is allegedly identical to that of Falcon 9,
don't
they already have full performance data on it?

Not in this configuration.

So what is different in terms of Stage 2's performance if the hardware
is identical?

It's being launched on by Falcon Heavy lower stages, not a Falcon 9
first stage.

USAF is certifying Falcon Heavy for launches, so they want to test the
entire system "end to end".

I have no doubt they want to do that. They need to test separation, and
they will want Stage 2 to get away from Stage 1 before stage 1 goes
down, and there is also the issue of testing software/command/control etc.

However, my question pertains to performance. If Stage 2 is identical to
previously flown one, in what way would its performance once detached
from Stage1 be any different?

The stage surely can provide the same delta-V, but it has a completely
different starting point. Falcon 9 stages pretty early and relies on
the upper stage to provide a lot of the delta-V. On Heavy, it will
stage higher and faster, so they might eek out a tad more performance
due to less atmosphere (better engine performance at the beginning of
2nd stage burn and less air drag).

Again, they're testing the overall performance of Falcon Heavy. That
means testing the whole thing.

USAF doesn't much care about landings, unless it screws up their launch.
So SpaceX wants to test the entire system "end to end", including
landings so that the USAF will have confidence in the entire system,
including landings.

Actually USAF would care about landings if it means that their launch
costs are an order of magnitude lower when SpaceX gets to land the
stages back.

My point is USAF doesn't give a damn how SpaceX reduces costs. Whether
through cheaper manufacturing or reuse, they don't care as long as the
launches are successful.

Yep, another small amount there as well. The program was pretty
desperate to reduce mass on the orbiter and the ET. They were scrubbing
mass from the most insignificant of things to save a kg or two here and
there.

BTW, common for all flying aircraft. And even during production,
Boeing/Airbus work to reduce weight of aircraft. And airlines shave
weight too (plastic cutlery for coach for instance).

If you look at all the performance upgrades, and the increased payload
to LEO they provided, everything was relatively small, except for the
aluminum-lithium Super Lightweight External Tank. That was the one big
bang for the buck improvement made to the system. Even then, it wasn't
much. Modules for ISS were smaller than planned for Freedom and they
had to be launched mostly empty of racks, which had to be brought up on
later flights. That's why it took so damn many shuttle flights to build
and outfit the US side of ISS.

Moving the orbit from KSC's natural inclination to that of the Russian
launch site really, really hurt performance of the shuttle.

It depends on Q, which is the dynamic pressure experienced at the speed
and altitude that the boosters drop off. It'll be higher than SRB sep
on the shuttle, but will surely be faster as well.

But based on the videos that SpaceX had released from a recovered
fairing while it was floating in space, it appears to be a very non
violent environment at that speed.

Payload fairings are necessarily very large and very light. Also they
have a propulsion package (reaction control jets) on those fairings to
aid in reentry and recovery. It's not at all as simple as it seems.

Isn't it correct to assume that separation of boosters will happen at
roughlty the same altitude/speed compared to stage 1 separation for
Falcon 9?

Devil's in the details. We're close enough to launch time that it's
easiest to wait and see from the launch video what the numbers will
actually be instead of arguing about it here.

Jeff
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All opinions posted by me on Usenet News are mine, and mine alone.
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Le Jan/31/2018 Ã* 6:08 AM, Jeff Findley a écritÂ*:
In article ,
says...

On 2018-01-30 06:09, Jeff Findley wrote:

That and if you're aiming for an escape trajectory, you don't care how
low "perigee" is, because you're never going to experience it. So why
waste fuel on raising it about the ground at all?

Side question:

If you are in orbit for a few hours and then leave to Jupiter and
beyond. Does spending fuel to circularize that orbit at apogee for those
few hours end up reducing fuel needed once you fire engines to get to
espape velocity?

No. That's why I said in a previous post it is a waste to do so if your
goal is to get past earth escape velocity. I took a 500 level orbital
mechanics class when I was at Purdue. It was surely the 2nd hardest
class I ever took. Professor Howell, who taught the class, came to
Purdue from JPL where she used to simulate trajectories of planetary
missions, including planetary fly-bys. I remember a few things from
that class.

It's not going to be in a circular orbit. It's going to be in a
Hohmann
transfer orbit between earth's orbit and Mars' orbit. It's just that
Mars won't be there when it gets there. Presumably earth won't be there
either

Hohmann, from what that Internet thing tells me is to transfer from one
circular to another circular orbit and requires a burn once you reach
the destination altitude to "stay there".

I said it's going into a Hohmann transfer orbit. Then it's done because
no more battery power and no more fuel in the Falcon upper stage. The
upper stage with the car attached will stay in that Hohmann transfer
orbit, continuously cycle between earth's orbit and Mars' orbit, until
something else perturbs its orbit. My guess is that it will eventually
be perturbed by either earth or Mars and then who knows what it's going
to do because it will depend on the exact details of the interaction.
Again, orbital mechanics is not easy.

If the Tesla is going to be in elliptical orbit with perigee at Earth
and Apogee at Mars altitudes, doesn't that have a risk that it will come
back to Earth at some point ?

If it is possible depends on the details of the final orbit. Again,
we'll have to wait until it's in that orbit to predict what might
happen.

If this happens it will almost surely burn up on reentry. **** falls to
earth all the time. It's not like this thing is huge like Skylab.

(this is in a context of battery autonomy and ability to fire engines
much later to at least raise perigee to above earth's orbit around sun)

Batteries will be dead long before that. And any LOX in the oxidizer
tank will have boiled off completely as well. You're not going to do
anything with a dead battery and only kerosene fumes in the fuel tank.

I don't know how to put this any more clearly. There will never be a
circularization burn at Mars' orbital distance. There simply can't be.
it's just not physically possible using the stock Falcon upper stage
with Merlin engine.

Since second stage is allegedly identical to that of Falcon 9,
don't
they already have full performance data on it?

Not in this configuration.

So what is different in terms of Stage 2's performance if the hardware
is identical?

It's being launched on by Falcon Heavy lower stages, not a Falcon 9
first stage.

USAF is certifying Falcon Heavy for launches, so they want to test the
entire system "end to end".

I have no doubt they want to do that. They need to test separation, and
they will want Stage 2 to get away from Stage 1 before stage 1 goes
down, and there is also the issue of testing software/command/control etc.

However, my question pertains to performance. If Stage 2 is identical to
previously flown one, in what way would its performance once detached
from Stage1 be any different?

The stage surely can provide the same delta-V, but it has a completely
different starting point. Falcon 9 stages pretty early and relies on
the upper stage to provide a lot of the delta-V. On Heavy, it will
stage higher and faster, so they might eek out a tad more performance
due to less atmosphere (better engine performance at the beginning of
2nd stage burn and less air drag).

Technically true, but the staging on a Falcon 9 is already basically in
vacuum. The difference between staging at 3 Pa of pressure (0.00003
atmosphere) as a typical Falcon 9 launch would do and complete vacuum is
not significant. So your *tad* more performance is really a very small
tad.


Alain Fournier