BFR early next year.

On 18-03-18 15:56 , Jeff Findley wrote:
In article ,
says...
...
In a "Pan Am flight 006 to Mars and back, would the mass of the vehicle
making the drop from space and land to surface be roughly the same ? Or
would landing at one planet require much more fuel?

You'd need a lot more fuel and oxidizer to land on Mars since Mars
atmosphere is so thin you won't get anywhere near as much aerodynamic
braking as you get on earth.

Hmm. In his "Making Life Multiplanetary" address in September 2017, Musk
showed a simulation of a BFS Mars landing with text saying "over 99% of
energy removed aerodynamically". If less than 1% of the orbital energy
remains for rocket braking, is that really a significant difference
between Mars and Earth?

--
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
. @ .

On Mar/18/2018 at 2:32 PM, Niklas Holsti wrote :
On 18-03-18 15:56 , Jeff Findley wrote:
In article ,
says...
** ...
In a "Pan Am flight 006 to Mars and back,* would the mass of the vehicle
making the drop from space and land to surface be roughly the same ? Or
would landing at one planet require much more fuel?

You'd need a lot more fuel and oxidizer to land on Mars since Mars
atmosphere is so thin you won't get anywhere near as much aerodynamic
braking as you get on earth.

Hmm. In his "Making Life Multiplanetary" address in September 2017, Musk
showed a simulation of a BFS Mars landing with text saying "over 99% of
energy removed aerodynamically". If less than 1% of the orbital energy
remains for rocket braking, is that really a significant difference
between Mars and Earth?


One percent of the energy of Mars' escape velocity (escape not
orbital energy, I think that is the relevant value to use here)
means one tenth its speed. That's about 503 m/s. According to
https://www.reddit.com/r/spacex/comm...tegy_analysed/
or https://tinyurl.com/hk252mj
the falcon 9 first stage inbound at 1.1 km travels at 105 m/s.
So 5 times the speed, 23 times the energy on Mars vs Earth.

I'd say it is significant but not a big problem. Of course, less
than 1% leaves plenty of room, 0.1% is less than 1%. But I would
think that it would be close to 1%, 5 times the speed seems
reasonable to me.


Alain Fournier

In article ,
lid says...

On 18-03-18 15:56 , Jeff Findley wrote:
In article ,
says...
...
In a "Pan Am flight 006 to Mars and back, would the mass of the vehicle
making the drop from space and land to surface be roughly the same ? Or
would landing at one planet require much more fuel?

You'd need a lot more fuel and oxidizer to land on Mars since Mars
atmosphere is so thin you won't get anywhere near as much aerodynamic
braking as you get on earth.

Hmm. In his "Making Life Multiplanetary" address in September 2017, Musk
showed a simulation of a BFS Mars landing with text saying "over 99% of
energy removed aerodynamically". If less than 1% of the orbital energy
remains for rocket braking, is that really a significant difference
between Mars and Earth?

If that number is correct, perhaps not. The devil will be in the
details though.

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 Mar/18/2018 at 2:32 PM, Niklas Holsti wrote :
Hmm. In his "Making Life Multiplanetary" address in September 2017, Musk
showed a simulation of a BFS Mars landing with text saying "over 99% of
energy removed aerodynamically". If less than 1% of the orbital energy
remains for rocket braking, is that really a significant difference
between Mars and Earth?


One percent of the energy of Mars' escape velocity (escape not
orbital energy, I think that is the relevant value to use here)
means one tenth its speed. That's about 503 m/s. According to
https://www.reddit.com/r/spacex/comm...tegy_analysed/
or https://tinyurl.com/hk252mj
the falcon 9 first stage inbound at 1.1 km travels at 105 m/s.
So 5 times the speed, 23 times the energy on Mars vs Earth.

I'd say it is significant but not a big problem. Of course, less
than 1% leaves plenty of room, 0.1% is less than 1%. But I would
think that it would be close to 1%, 5 times the speed seems
reasonable to me.

That looks like a pretty good first approximation. But secondary
effects like gravity losses will be different because the two planets
have different gravity.

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 on Sun, 18 Mar 2018
09:46:42 -0400:

In article ,
says...

On 2018-03-17 02:59, Fred J. McCall wrote:

What are you gibbering about now?

Enterprise was built in another era. No CAD/CAM and no experience in
building a flying rocket.


Irrelevant. The A-12, SR-71 Blackbird, X-15, XB-70, and a host of other
aircraft and rocket powered winged vehicles were designed before
CAD/CAM. You don't seem to have a point here. CAD isn't a panacea or
silver bullet. It's a design tool, nothing more. CAM is the same.
Very skilled machinists can do almost everything that CAM can do.
Again, it's a manufacturing tool, nothing more.


In point of fact, things tend to be built to finer tolerances when
done by hand. Relying on the machines means leaving a little more
'meat' on the parts to make sure everything fits.



Enterprise was needed not only use to test
gliding/landing but also to develop/test mounting on the full stack, as
well as firing SRBs to measure vibration.

The knowledge gained from it resulted in a production design
sufficiently different that it wasn't worth retrofitting Enterprise.


You're misrepresenting the facts here. The fact was that it was going
to be more work to dismantle Enterprise and refit it than to build upon
STA-99 which was nothing more than structure anyway (structural test
articles are like that you know).


Such misrepresentation is pretty much a given with Mayfly. I honestly
wonder if he does it on purpose or if he really doesn't remember
anything.


Plus they had not yet gained the sensor data from flying Columbia to
orbit and back. That gave them the information they needed to lighten
the structure, not Enterprise's relatively mild glide landings.
Columbia's data covered launch (including being shaken by the SRBs),
max-Q, and reentry. Enterprise only provided subsonic flight data and
landing data.


Columbia was about 4 tons heavier that the last orbiters built.



BFS, on the other hand tests a fully functioning rocket capable of
taking off and landing. Engines, tanks, software, aerodynamic
controls/paddles, landing gear ad its deployment using real actuators
(Enterprise used explosive bolts) etc. (not sure if it will have side
thrusters for attitude control)


Sure, it will lack a payload, crew compartment, ECLSS etc. But from the
rocket point of view, it should be a fairly functional system.

Furthermore, it is an evolution from experience gained from Falcon 9
whereas the Shuttle was truly the "undiscovered Country" since it was
not an evolution from Apollo systems/designs.


You must be completely forgetting the myriad of research vehicles
between the USAF and NASA which were targeted at eventually making an
operational spacecraft that could reenter and land on a runway. Several
of these designs flew on top of launch vehicles and performed unmanned
reentries. There are a few sitting in the USAF Museum in Dayton Ohio.
Check their website. They'll have pictures and summaries of each
online. You might learn something.

The fact is that the space shuttle orbiter design was *not* created in a
vacuum.


Yep. There was a LOT of lifting body research prior to the design of
the Shuttle Orbiter.

You don't need the vacuum engines to lift off and land. You do need
some if you're planning on going clear to space, but even then you
probably don't need all of them until you start flying heavy cargos.


Montréal got some new Métros about 2 years ago. Previous generation was
designed in early 1970s. Alstom got the contract for the bogies/motors
and went with a fancy pneumatic suspension as well as the tires for our
métro.

All built to fit the existing tunnel dimensions, platform height and
loading gauge.

BUT... during testing, the STM (transit company)discobered that if the
tires blew AND the penumatic suspension lost pressure, a car could sway
enough to rub against tunnel walls in some areas. (previous generation
had spring suspension, so failure of suspension had not been something
they worried about when defining the specs of the vehicle).


WTF does any of this have to do with a VTVL TSTO?


I'm sure somewhere in his tiny mind it devastatingly proves how he is
right and we are wrong.

They may very well make the first BDF launch without vacuum engines.
But
this would not validate things very well. If the goal is to validate the
design, and if the vacuum engines are Raptor engines with different
bells, they may want to load them up. (or peruaps load early production
Raptors with vacuum bells to occupy the space and weigfht.

Maybe. Or they could test incrementally (like they always seem to do).
Grasshopper certainly wasn't equipped with 9 Merlin engines. It wasn't
even equipped with the final design of the landing legs. It didn't need
either of them to fly and gather the data they needed.


He doesn't seem to understand how testing works. Because it is
reusable, it will likely be tested just like an airplane, which means
they'll test it pretty much as you describe; baby steps followed by
slowly opening up the envelope.


I'm sure the SpaceX engineers understand the trades with the first
BFR/BFS stages better than we do.


HERESY! Even Elon Musk doesn't understand it as well as Mayfly!

Prior to launch, they can then test that interaction between engine
bells is within specs in all failure modes, and that a vacuum bell stuck
in the worng orientation won't prevent a launch engine from gaving full
gimball movement. (expecially needed for landing when rapid changes are
needed).

Not sure what you're yammering on about.


Mayfly thinks they just paste the engines on in any old configuration
that looks good to them and don't consider actually operating them
until they're ready to fly the thing.

If you don't need the heat shield then you don't need the vacuum
engines.

The heat shield is just fancy outside skin. Vacuum engines are mounted
amongst launch/landing engines so ensuring the whole engine "pod" works
even when half the engines are not fired is important.

You don't have anything to back up this hand waving.


And he doesn't seem to realize that the engines aren't just packed in
there randomly.

Also, assuming BFS 1,0 does not result in fireworks, the work done to
assemble a more complete vehicle would be of use for its second flight.
(and one would have to do risk management to decide wether to mount good
vacuum engines, or duds from early production but with proper vaccum bells.)

SpaceX will no doubt do many small hops with version 1 of the vehicle.
They're not going to do one small hop and declare they're ready to go to
orbit. That's not how they work. Build a little, test a little, fly a
little. Iterative. That's how they work.


He doesn't understand that that's how all flying vehicle engineers
work. Watching the testing of a new fighter aircraft is pretty boring
until you get toward the end of the testing where they're pushing the
boundaries of the flight envelope, testing for controlled departures,
etc. The first months can be hideously boring, consisting of things
like driving around on the ground, a few minutes of flight in the
heart of the envelope, etc.


Version 2 won't fly until they've gathered all the data they need from
version 1. So, version 1 may or may not be equipped with a full
compliment of Raptor engines, a combination of real and dummy engines.
That's up to the SpaceX engineers to decide.


But ... but ... MAYFLY!

And depending on software, I could see a case for needing the vaccum
engines in the event that sea leavel engines fail during landing.
(depending on where in teh cluster those engines are located).

No, you can't fire the vacuum engines and use them for landing. You'd
get flow separation and the bells might very well destroy themselves,
which wouldn't make for a very safe landing when your engines are
literally falling apart.

Besides, that's why there will be three Raptor engines in the center,
for redundancy during landing.


Is it fair to expect Mayfly to actually know anything about the
vehicle or bother to look it up when he has such a large store of
handwavium to draw on?

So just because the grasshoper tests doesn't require vacuum engines on
paper doesn't mean that they won't want to have them on for the test
because integrating as many compotents as possible is a better test.

We'll see, but I seriously doubt that they'd bolt a bunch of engines
that aren't needed on the test vehicle. Those engines aren't free you
know. Why risk millions of dollars in engines you don't need on a test
flight? Makes no sense unless you really do need them, which they
don't.


That's what I think, too. They won't bother with those engines until
they're ready to fully validate the guide laws and need accurate
moment arms and CGs. Even then they might just bolt in some weights
until they're ready to fly to space.

I don't know why you're so wrapped around the axle about the
damned tank, since we all know that's done.

Enterprise didn't have fully functioning tanks. Didn't have its real
fuel cells and O2/H2 tanks, didn't have hypergolics. BFS will have fully
functional tanks. So it is far ahead in terms of moving from "idea" to
"product" then Enterprise was.

All those systems you mention on Enterprise weren't needed for subsonic
flight of the vehicle. Not including them on Enterprise made sense. If
the first BFR/BFS test vehicle is only making "short hops" it won't need
vacuum engines. Not including real vacuum engines on the test vehicle
might make sense in the very same way.


As Elon Musk said, leaving out the vacuum engines for initial testing
gives you a much better fuel margin. This tells me that except for
things that are designed to be added later (engines, heat shield) the
dry mass of the first test vehicle will be pretty close to the final
vehicle.

And this is why advancing first flight is significant because first
flight really needs to have a lot of the final systems finalized.

Depends on how high the "hop" is. If it's not high enough to need
vacuum engines, why include them in the test?


First test will be under five miles slant range, according to Musk

No, it was designed as a test article, which is not the same thing.

Test article for something that had never been done before. And with
many changes made as it was being developped (liquid fltyback boosters
abandonned etc).

This is gobbledygook. The configuration of the STS was finalized long
before any metal was bent. That included the SRBs and drop tank (ET).
The size of the orbiter's payload bay and payload mass was set as well.


What? You mean engineers don't just build random **** and then figure
out if it works?

While the payload of BFS (aka: crew compartment for 100 passengers) is
likely going to change a lot from early concepts, the propulsion/tanks
portion as lower structures are likely to be fairly close to final
designs with tweaks over time. (as has happened with Falcon 9).

Untrue. Block 5 Falcon 9 has many significant differences when compared
to Falcon 9 V 1.0. Not all are visible from the outside but things like
the height of the vehicle, changing the engine configuration from a
square to the "octoweb", and the inclusion of landing legs and grid fins
are externally visible.

https://en.wikipedia.org/wiki/Falcon_(rocket_family)

Most important is the sheer size of the vehicle and engine improvements.
Improvements to Merlin allowed tank stretches and overall performance
improvements over V 1.0. Part of the reason Falcon Heavy kept getting
delayed is that Falcon 9 kept getting higher payload capacity and could
therefore launch some payloads originally intended for Falcon Heavy.


Damn that pesky reality blowing apart Mayfly's handwavium castles!

Horse****. They didn't design the thing using bearskins and stone
axes, you know.

When you look at the history of the shuttle, there was a lot that wasn't
predicted while it was being designed. Understanvbly so since this was
something that had never been done before. Re-usable design, totally
different stack at launch pad, totally different landing, HUGE crew
cabin from before, new materials, new heat shield etc etc. With each
delay, each incident and the 2 losses, failure modes that had not been
predicted during design crept up.

This is nonsense. As I said before, the overall configuration was fixed
long before metal was bent. You really need to read this book:

Space Shuttle: The History of the National Space Transportation System
The First 100 Missions Hardcover - May 11, 2001
by Dennis R. Jenkins (Author)
https://www.amazon.com/Space-Shuttle...ransportation-
Missions/dp/0963397451


What? You expect him to actually inform himself about the facts?
Unheard of!

In the case of BFR/BFS, Musk is scaling the experience of Falcon 9 as a
core, and adding new stuff like heat shield, and re-usable second stage
(BFS). landing and re-usability have already been tested. (and Falcon 9
learned from the experience of the difficult re-usability of Shuttle).

So first flight of BFS will incorporate systems/experience that will
make it a far more complete ship compared to eventual production than
Enterprise was compared to the production Shuttles.

That's because Enterprise was only the orbiter. The SRBs and the ET
made up 95% of the launch part of the system. The orbiter only
contained the flight computers, SSMEs, and the OMS pods. Everything
else needed for launch dropped off before the shuttle got to orbit.

BFR/BFS isn't going to dispose of any parts. It's quite different than
the space shuttle in that regard. So some of the shuttle experience
simply won't apply because it's just not the same.


I don't think Mayfly can tell the difference between a testing
philosophy and actual detail differences between vehicles.


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

Jeff Findley wrote on Sun, 18 Mar 2018
09:56:23 -0400:


BFS will have three sea level engines for landing. But the extras are
mostly there for redundancy. Depending on the payload, I'd think one
would be sufficient in most cases, even on earth. Raptor will have
about 400,000 lbf thrust at landing. Dry mass of BFS is reported to be
about 200,000 lbs. A "typical" payload at landing is reported to be
110,000 lbs. So one Raptor is all that's needed for a "typical"
landing.

Of course, these numbers might change over time with block upgrades,
just as they did for Falcon 9.


Actually BFS initially might have trouble with single engine landings
until they get the follow-on block of Raptor engines with 20% more
performance.


--
"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

On Mar/18/2018 at 4:58 PM, Jeff Findley wrote :
In article , says...

On Mar/18/2018 at 2:32 PM, Niklas Holsti wrote :
Hmm. In his "Making Life Multiplanetary" address in September 2017, Musk
showed a simulation of a BFS Mars landing with text saying "over 99% of
energy removed aerodynamically". If less than 1% of the orbital energy
remains for rocket braking, is that really a significant difference
between Mars and Earth?


One percent of the energy of Mars' escape velocity (escape not
orbital energy, I think that is the relevant value to use here)
means one tenth its speed. That's about 503 m/s. According to
https://www.reddit.com/r/spacex/comm...tegy_analysed/
or https://tinyurl.com/hk252mj
the falcon 9 first stage inbound at 1.1 km travels at 105 m/s.
So 5 times the speed, 23 times the energy on Mars vs Earth.

I'd say it is significant but not a big problem. Of course, less
than 1% leaves plenty of room, 0.1% is less than 1%. But I would
think that it would be close to 1%, 5 times the speed seems
reasonable to me.

That looks like a pretty good first approximation. But secondary
effects like gravity losses will be different because the two planets
have different gravity.

Yes but those secondary effects are very small to the point that
they can be ignored. Gravity loss in the last few meters are negligible.
Gravity loss before the last few meters are taken care of be air drag.


Alain Fournier

On Mar/18/2018 at 5:59 PM, Alain Fournier wrote :
On Mar/18/2018 at 4:58 PM, Jeff Findley wrote :
In article , says...

On Mar/18/2018 at 2:32 PM, Niklas Holsti wrote :
Hmm. In his "Making Life Multiplanetary" address in September 2017,
Musk
showed a simulation of a BFS Mars landing with text saying "over 99% of
energy removed aerodynamically". If less than 1% of the orbital energy
remains for rocket braking, is that really a significant difference
between Mars and Earth?


One percent of the energy of Mars' escape velocity (escape not
orbital energy, I think that is the relevant value to use here)
means one tenth its speed. That's about 503 m/s. According to
https://www.reddit.com/r/spacex/comm...tegy_analysed/

or https://tinyurl.com/hk252mj
the falcon 9 first stage inbound at 1.1 km travels at 105 m/s.
So 5 times the speed, 23 times the energy on Mars vs Earth.

I'd say it is significant but not a big problem. Of course, less
than 1% leaves plenty of room, 0.1% is less than 1%. But I would
think that it would be close to 1%, 5 times the speed seems
reasonable to me.

That looks like a pretty good first approximation.Â* But secondary
effects like gravity losses will be different because the two planets
have different gravity.

Yes but those secondary effects are very small to the point that
they can be ignored. Gravity loss in the last few meters are negligible.
Gravity loss before the last few meters are taken care of be air drag.

I should add that things would be different if you didn't have
sufficient thrust. If you fire your engines for two minutes to
to cancel that 503 m/s then the gravity loss isn't negligible.
But if you do like falcon 9 boosters do and decelerate rapidly
just before touching the ground then gravity loss is negligible.


Alain Fournier

Alain Fournier wrote on Sun, 18 Mar 2018
19:35:57 -0400:

On Mar/18/2018 at 5:59 PM, Alain Fournier wrote :
On Mar/18/2018 at 4:58 PM, Jeff Findley wrote :
In article , says...

On Mar/18/2018 at 2:32 PM, Niklas Holsti wrote :
Hmm. In his "Making Life Multiplanetary" address in September 2017,
Musk
showed a simulation of a BFS Mars landing with text saying "over 99% of
energy removed aerodynamically". If less than 1% of the orbital energy
remains for rocket braking, is that really a significant difference
between Mars and Earth?


One percent of the energy of Mars' escape velocity (escape not
orbital energy, I think that is the relevant value to use here)
means one tenth its speed. That's about 503 m/s. According to
https://www.reddit.com/r/spacex/comm...tegy_analysed/

or https://tinyurl.com/hk252mj
the falcon 9 first stage inbound at 1.1 km travels at 105 m/s.
So 5 times the speed, 23 times the energy on Mars vs Earth.

I'd say it is significant but not a big problem. Of course, less
than 1% leaves plenty of room, 0.1% is less than 1%. But I would
think that it would be close to 1%, 5 times the speed seems
reasonable to me.

That looks like a pretty good first approximation.* But secondary
effects like gravity losses will be different because the two planets
have different gravity.

Yes but those secondary effects are very small to the point that
they can be ignored. Gravity loss in the last few meters are negligible.
Gravity loss before the last few meters are taken care of be air drag.

I should add that things would be different if you didn't have
sufficient thrust. If you fire your engines for two minutes to
to cancel that 503 m/s then the gravity loss isn't negligible.
But if you do like falcon 9 boosters do and decelerate rapidly
just before touching the ground then gravity loss is negligible.


This is intended to be a manned vehicle. As such, they won't want any
sustained g loads above about 3g (and lower is better). Unless you
restrict wetware to trained military folks in peak condition, that's
really the desired 'limit'. Soyuz peaks at around 4-4.5g for brief
periods of time during takeoff and landing. Shuttle deliberately
managed engine power to not exceed 3g. Falcon 9 hits around 3.5g
during launch (and throttles back in order to do that). Mercury and
Gemini were pretty ugly, with peak loads above 7g. Mercury took
almost 11g on reentry and jolt much higher. But they launched on
ICBMs which weren't optimized to give the wetware a tolerable ride and
were all military test pilots. Apollo hit something like 6g on the
return from the Moon.


--
"Insisting on perfect safety is for people who don't have the balls to
live in the real world."
-- Mary Shafer, NASA Dryden

Le Mar/18/2018 Ã* 9:10 PM, Fred J. McCall a écritÂ*:
Alain Fournier wrote on Sun, 18 Mar 2018
19:35:57 -0400:

On Mar/18/2018 at 5:59 PM, Alain Fournier wrote :
On Mar/18/2018 at 4:58 PM, Jeff Findley wrote :
In article , says...

On Mar/18/2018 at 2:32 PM, Niklas Holsti wrote :
Hmm. In his "Making Life Multiplanetary" address in September 2017,
Musk
showed a simulation of a BFS Mars landing with text saying "over 99% of
energy removed aerodynamically". If less than 1% of the orbital energy
remains for rocket braking, is that really a significant difference
between Mars and Earth?


One percent of the energy of Mars' escape velocity (escape not
orbital energy, I think that is the relevant value to use here)
means one tenth its speed. That's about 503 m/s. According to
https://www.reddit.com/r/spacex/comm...tegy_analysed/

or https://tinyurl.com/hk252mj
the falcon 9 first stage inbound at 1.1 km travels at 105 m/s.
So 5 times the speed, 23 times the energy on Mars vs Earth.

I'd say it is significant but not a big problem. Of course, less
than 1% leaves plenty of room, 0.1% is less than 1%. But I would
think that it would be close to 1%, 5 times the speed seems
reasonable to me.

That looks like a pretty good first approximation.Â* But secondary
effects like gravity losses will be different because the two planets
have different gravity.

Yes but those secondary effects are very small to the point that
they can be ignored. Gravity loss in the last few meters are negligible.
Gravity loss before the last few meters are taken care of be air drag.

I should add that things would be different if you didn't have
sufficient thrust. If you fire your engines for two minutes to
to cancel that 503 m/s then the gravity loss isn't negligible.
But if you do like falcon 9 boosters do and decelerate rapidly
just before touching the ground then gravity loss is negligible.


This is intended to be a manned vehicle. As such, they won't want any
sustained g loads above about 3g (and lower is better). Unless you
restrict wetware to trained military folks in peak condition, that's
really the desired 'limit'. Soyuz peaks at around 4-4.5g for brief
periods of time during takeoff and landing. Shuttle deliberately
managed engine power to not exceed 3g. Falcon 9 hits around 3.5g
during launch (and throttles back in order to do that). Mercury and
Gemini were pretty ugly, with peak loads above 7g. Mercury took
almost 11g on reentry and jolt much higher. But they launched on
ICBMs which weren't optimized to give the wetware a tolerable ride and
were all military test pilots. Apollo hit something like 6g on the
return from the Moon.

Yes, especially after a few months of travel between Earth and Mars
you have to take that into consideration. But this would be only
for a few seconds. I think say 4g for 13.5 seconds should be OK,
it's enough to decelerate from 503 m/s and the gravity loss is small.


Alain Fournier