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  #11  
Old January 5th 20, 03:05 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default What to expect

In article ,
says...

On 2020-01-04 10:40, Jeff Findley wrote:

No, because that propellant is needed in case of a launch abort.


I was asking on whether propellant used for abort = propelland needed
for propulsive landing. Aka: had SpaceX been allowed propulsive landing,
would the fuel tanks for the super dracos have been bigger?


No. I clearly explained this in detail, but here it is again:

If the propellant is used for abort, there is none left for propulsive
landing. Which doesn't matter anyway, because an abort puts Dragon 2
over the ocean anyway. So in an abort, you'd use parachutes and splash
down in the ocean.

With regards to landing gear: I have to wonder if that might not have
been the show stopper for NASA. Mechannically deployed landing legs seem
like a accident begging to happen if one fails to deploy/lock.


It wasn't.

BTW, did the shuttle crew have cranks to manually lower the landing
gears like on planes at some point in time? Or is the time between
landing gear deployment and touching ground so short that it was
pointless to add manual gear deploy cranks?


No. In a contingency (e.g. no hydraulic power to lower the landing
gear), there were pyros which would operate what amounted to pneumatic
cylinders which would force the gear down. Clearly "one time use", but
in an emergency, it's better than crashing into the runway without
landing gear.

Note that the orbiters could NOT safely belly land due to the thermal
tiles literally "digging into the runway" and creating way too much
friction. Simulations indicated this would cause the orbiter to
pinwheel out of control and off the runway. So if all three landing
gear did not deploy *and* lock, it was a "very bad day" (loss of orbiter
and crew).

a propulsive landing. In the event of a launch abort, Dragon 2 would
have used parachutes to splash down in the ocean.


Can Starliner launch over land if after an abort, the combination of
parachutes and inflatable mattress lets it land anywhere?


Doesn't matter because Atlas V would never be allowed to launch over
land. Dropping stages on land is something that only Russia and the
Chinese do. All other countries drop their expendable stages in the
ocean.

insertion propellant. And in the case of a complete failure of
Starliner to perform that orbital insertion burn, it will simply reenter
as Atlas V puts it into an orbit whose low point is within the earth's
atmosphere.


So in the context of the recent Starliner test launch, how long after it
detached from Atlas and failed to activate orbit insertion engines,
would Starliner have re-entered? a few orbits or at the next perigee?


As I said, the low point of the orbit was *inside* the atmosphere. So
it would reenter without really completing that single orbit.

Just curious how close to re-entry the ship was at the time ground
control re-established contact with it and started to "fix" it. I take
it a "confused" ship left to its own devices would have re-entered with
its service module still attached and not have realised it was
re-entering and not deployed parachutes?

(since its software seems so based on a timer).


In retrospect, the decision to have Atlas V *not* put Starliner into a
"stable orbit" was a bad one. But, it was a trade based on all the
possible failure scenarios and it automatically put the Centaur upper
stage on a destructive reentry so that there was zero chance it would
not destructively reenter.

Jeff
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  #12  
Old January 5th 20, 03:19 PM posted to sci.space.policy
Jeff Findley[_6_]
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Default What to expect

In article ,
says...

On 2020-01-04 21:40, Greg (Strider) Moore wrote:

No, you're missing the point. The propellant was for one OR the other.


I understand that. Rephrasing my question:

Propellant tanks would be sized for the biggest needs of abort OR
landing. If landing requires more fuel than an abort, then the tanks
would be sized to support landing.

In such a scenario, removing propulsive landing would allow SpaceX to
shrink the propellant tanks for super dracos to only be able to do aborts.

If both functions need the same amount of fuel, then removing landing
doesn't change tank size. (same if Abort uses more fuel than landing at
which point those tanks are sized to meet the needs of the abort function).


In either case having a propellant reserve is a "good thing". You might
rephrase the question as which would have had a bigger reserve. But you
won't get an answer. This is because SpaceX will have tested both a pad
abort and an in flight abort, so they'll have solid numbers for that.

But, for propulsive landing, they'll only have simulations and some
ground testing to determine how much propellant is required. Without
actually testing propulsive landing (repeatedly in different situations
like varying wind speed), they can't be 100% confident in exactly how
much reserves they'd have in a landing scenario.

The big picture question:

Say Dragon2 has proven itself. How difficult would it be for SpaceX to
build a prototype that can propulsively land? If tanks already big
enough, then it is a matter of adding the landing gear and changing
software.


Yes, but they *won't* do this because the customer, NASA, simply doesn't
want this and won't pay for this.

snip

I know NASA was rather paranoid about handing a returning ship that
still have traves of hydrazine in it. Has SpaceX solved the issue or
will it also have to be paranoid when processing a returning capsule to
be refurbished for the next flight?


As far as I know, SpaceX will be building new Dragon 2 capsules for each
crew flight. Maybe, eventually, they'll start refurbishing Dragon 2
capsules for crew use, but that's not currently in the plan.

I take it they still have to empty the tanks and refill for each flight,
or could tehy leave fuel in the tanks during refurbishement as long as
it isn't its "best before" date ?


You don't work on spacecraft when it has extremely toxic/flammable
hypergolics in the tanks. This also applies to high pressure helium in
the pressurant tanks. They'd all be completely drained after flight,
just like on the shuttle orbiter post-landing.

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.
  #13  
Old January 5th 20, 03:24 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default What to expect

In article ,
says...

In article ,
says...
BTW, did the shuttle crew have cranks to manually lower the landing
gears like on planes at some point in time? Or is the time between
landing gear deployment and touching ground so short that it was
pointless to add manual gear deploy cranks?


No. In a contingency (e.g. no hydraulic power to lower the landing
gear), there were pyros which would operate what amounted to pneumatic
cylinders which would force the gear down. Clearly "one time use", but
in an emergency, it's better than crashing into the runway without
landing gear.


Here is a cite:

LANDING/DECELERATION SYSTEM
http://www.spaceshuttleguide.com/sys...n_system.htm#L
anding_Gear_Doors

Note how complicated all of this is. Lots of redundancy and backups
built into the system because it *had* to work or the crew was dead.
Unfortunately, all that complexity drives up costs.

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.
  #14  
Old January 5th 20, 04:45 PM posted to sci.space.policy
Alain Fournier[_3_]
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Posts: 548
Default What to expect

On Jan/5/2020 at 09:19, Jeff Findley wrote :
In article ,
says...

On 2020-01-04 21:40, Greg (Strider) Moore wrote:

No, you're missing the point. The propellant was for one OR the other.


I understand that. Rephrasing my question:

Propellant tanks would be sized for the biggest needs of abort OR
landing. If landing requires more fuel than an abort, then the tanks
would be sized to support landing.

In such a scenario, removing propulsive landing would allow SpaceX to
shrink the propellant tanks for super dracos to only be able to do aborts.

If both functions need the same amount of fuel, then removing landing
doesn't change tank size. (same if Abort uses more fuel than landing at
which point those tanks are sized to meet the needs of the abort function).


In either case having a propellant reserve is a "good thing". You might
rephrase the question as which would have had a bigger reserve. But you
won't get an answer. This is because SpaceX will have tested both a pad
abort and an in flight abort, so they'll have solid numbers for that.

But, for propulsive landing, they'll only have simulations and some
ground testing to determine how much propellant is required. Without
actually testing propulsive landing (repeatedly in different situations
like varying wind speed), they can't be 100% confident in exactly how
much reserves they'd have in a landing scenario.

The big picture question:

Say Dragon2 has proven itself. How difficult would it be for SpaceX to
build a prototype that can propulsively land? If tanks already big
enough, then it is a matter of adding the landing gear and changing
software.


Yes, but they *won't* do this because the customer, NASA, simply doesn't
want this and won't pay for this.


NASA is one customer. Bigelow or mister so and so might become other
customers. I think Mr Mezei's question here is pertinent. Other
customers might very well think that landing (on land) is preferable to
splashdown. Initially SpaceX was talking about having their Dragon
capsules do landings. I think they switched to splashdowns at the
request of NASA and not because there was some difficulty preventing
landings. I, like Mr Mesei, would like to know if going back to landing
is a possibility. Even if there were no difficulty preventing landings
early on in the design, it doesn't mean that going back to that scenario
now wouldn't basically implicate designing a new capsule. I don't know,
but I suspect it would mean a big design change. But possibly SpaceX
kept in mind all along that other customers might later ask for landing.

That said, I think that if SpaceX had kept its design compatible with
going back to landings, we would know about it. You don't design your
spacecraft with some interesting capabilities and don't tell anyone. If
you want to have customers, you shouldn't keep secret the capabilities
of your product. You keep secret how you managed to have those
capabilities but not the capabilities themselves.


Alain Fournier
  #15  
Old January 6th 20, 01:07 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default What to expect

In article , says...

On Jan/5/2020 at 09:19, Jeff Findley wrote :
In article ,
says...
The big picture question:

Say Dragon2 has proven itself. How difficult would it be for SpaceX to
build a prototype that can propulsively land? If tanks already big
enough, then it is a matter of adding the landing gear and changing
software.


Yes, but they *won't* do this because the customer, NASA, simply doesn't
want this and won't pay for this.


NASA is one customer.


Yes, but more importantly, NASA is the most important customer for
Dragon 2. In fact, it's the only customer who's paying for actual
Dragon 2 missions. All other customers are currently *potential*
customers.

Bigelow or mister so and so might become other customers.


Agree, *might*.

I think Mr Mezei's question here is pertinent. Other
customers might very well think that landing (on land) is preferable to
splashdown.


Yes, but only if they're going to actually *pay* to develop propulsive
landing. SpaceX proposed testing this using Dragon 2 cargo missions.
So to SpaceX, the cost of testing propulsive landings would have been
very small since they were going to fly those cargo missions *anyway*.
But because NASA is paying for those Dragon 2 cargo missions, and they
want to make sure they get valuable hardware back like EMU suits, NASA
balked at that proposal.

The problem is you can't really test propulsive landings with a crew on
board. So customers who want Dragon 2 for crewed flight would have to
pay for entire test flights of Dragon 2 propulsive landings. Maybe if a
customer like Bigelow agreed to do this with returning cargo missions to
their space stations it would work. And in the meantime, any crewed
missions paid for by Bigelow would still be splashing down int the
ocean.

Initially SpaceX was talking about having their Dragon
capsules do landings. I think they switched to splashdowns at the
request of NASA and not because there was some difficulty preventing
landings. I, like Mr Mesei, would like to know if going back to landing


See above. They switched because the customer, NASA, didn't want SpaceX
testing propulsive landings using returning cargo missions. If you can
find a source for other returning cargo missions where a different
customer will allow this sort of testing, it *may* be possible to
develop without spending a fortune on dedicated test flights.

That said, I think that if SpaceX had kept its design compatible with
going back to landings, we would know about it. You don't design your
spacecraft with some interesting capabilities and don't tell anyone. If
you want to have customers, you shouldn't keep secret the capabilities
of your product. You keep secret how you managed to have those
capabilities but not the capabilities themselves.


The biggest change was when SpaceX announced that cargo Dragon 2 would
*not* even have Super Dracos installed. This allows for more cargo mass
to be delivered to ISS. Any potential customer for Dragon 2 cargo
flights would have to sacrifice some cargo delivery capability on every
flight in order to test propulsive landings. At that point, it becomes
a cost trade.

In other words, is the extra cost of testing propulsive landings (in
terms of less cargo delivered on each flight) worth it in the long run
to this (currently hypothetical) new customer? On top of that, since
this would be a development program, there isn't certainty over how many
test flights would be needed to make the system safe enough to return
people. So there is risk that money would be spent to develop a
capability that might not ever mature.

And finally, you're talking about developing a capability NASA has
already made a hard pass on. That's an uphill battle to fight in and of
itself since they're the "experts" in crewed spaceflight. So, you've
got to find investors who will bet *against* NASA's "experts". This has
been a problem in the industry for decades. It has taken billionaires
with deep pockets to even start to break this cycle.

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.
  #16  
Old January 6th 20, 01:11 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default What to expect

In article ,
says...

On 2020-01-05 09:19, Jeff Findley wrote:

Yes, but they *won't* do this because the customer, NASA, simply doesn't
want this and won't pay for this.



If propulsive landing allows much checper re-use of capsule (no contact
with salt water), and ends up being far more convenient for NASA to have
SpaceX taxi drop them off at KSC, I could see NASA warming up to the
idea of allowing SpaceX to test propulsive landings.


They won't. Dragon 2 is already nearly half as expensive as Starliner.
If NASA were that interested in reducing costs further, they'd look to
Starliner, not Dragon 2.

Where there is a will, there is pork, and it wouldn't be surprising to
see NASA award contracts to research propulsive landings. (in the same
vein as NASA awarded to Boeing a contract to study all composite
aircraft fuselages).


Not when this becomes an *operational* program to perform crew rotations
for ISS. NASA becomes very risk averse when it comes to crewed
missions. They'll stick to what works.

SpaceX now has good experience landing rockets so NASA might be less
reluctant to allow research on this.


Actual evidence suggests otherwise. NASA refused to allow SpaceX to
test this using returning cargo Dragon 2 vehicles. The decision has
been made and NASA is quite unlikely to reverse that decision. When it
comes to operational missions, NASA is quite risk averse. The design of
Dragon 2 is "fully baked" and NASA won't change it now. To do so would
cost them time and money to recertify 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.
  #17  
Old January 6th 20, 01:19 PM posted to sci.space.policy
Jeff Findley[_6_]
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Posts: 2,307
Default What to expect

In article ,
says...

On 2020-01-05 09:19, Jeff Findley wrote:

But, for propulsive landing, they'll only have simulations and some
ground testing to determine how much propellant is required.


If the general design of the capsule was done at a time when they were
expecting to do propulsive landings, they would have had to estimate the
fuel needed for either abort or landing and choose the maximum of the
two to size the tanks.

If an abort requires much less fuel than landing, SpaceX may have shrunk
the tanks after NASA said "NO" to propulsive landing, at which point
building a Dragon with the bigger tanks needed to support landing might
require major redesign of the inside components.


If that were the case, and I'm not saying it is, it would be even
cheaper just to keep the tanks the same size and simply not fill them to
their maximum capacity. Making the tanks smaller would mean redesigning
not only the tanks, but their associated mounting hardware, plumbing,
and etc. All of those changes would require retesting, which isn't
cheap.

But if the existing tanks are capable of either abort or landing, then
adding propulsive landing would focus hardware work on the landing gear
only.


And I keep pointing out it's the cost of "certifying" propulsive
landings that's the roadblock, not the engineering details. There is
ample evidence that NASA won't pay. SpaceX clearly sees Dragon 2 as a
stepping stone to Starliner, so it won't spend any more development
money on Dragon 2.

So, *who* is going to pay to certify Dragon 2 propulsive landings? You
mentioned possible future customers like Bigelow Aerospace, but will
they pay the likely hundreds of millions of dollars required to develop
this? My guess is no. They'll likely be pinching any pennies they can
to keep actual missions to their space station as affordable as
possible.

In my mind no likely source of funding exists to pay for this, so it's
all theoretical.

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.
  #18  
Old January 6th 20, 04:21 PM posted to sci.space.policy
Niklas Holsti
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Posts: 168
Default What to expect

On 2020-01-06 14:19, Jeff Findley wrote:
SpaceX clearly sees Dragon 2 as a
stepping stone to Starliner, ...

Ahem. I assume you mean "Starship", don't you?

(Damn this hyperbolic fashion of using "star" in naming spacecraft not
designed for interstellar travel.)

--
Niklas Holsti
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niklas holsti tidorum fi
. @ .
  #19  
Old January 6th 20, 06:23 PM posted to sci.space.policy
Niels Jørgen Kruse[_2_]
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Default What to expect

Niklas Holsti wrote:

On 2020-01-06 14:19, Jeff Findley wrote:
SpaceX clearly sees Dragon 2 as a
stepping stone to Starliner, ...

Ahem. I assume you mean "Starship", don't you?

(Damn this hyperbolic fashion of using "star" in naming spacecraft not
designed for interstellar travel.)


Heh. The Starship is more of a Starliner than the Starliner.

The Starliner would more properly be named Starrowboat.

--
Mvh./Regards, Niels Jørgen Kruse, Vanløse, Denmark
 




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