Manned Dragon to land via rocket braking?

Pat Flannery wrote:
Rockets mounted in the RV would serve as both a full-envelope LES, and a
vertical landing system on return, though a reserve emergency parachute
system would still be carried.
Sounds complex, but innovative:
http://spaceflightnow.com/news/n1101/18spacex/
I always thought you could use the LES as a retrorocket system if you
designed it right, but the thought of using it as a landing system never
occurred to me.

I can't imagine they are envisioning replacing chutes entirely, even
though some of that article seems to suggest it. I mean that is a
rather decent quantity of propellant mass to do a "precise landing
under rocket power" no? Perhaps they plan on firing the LES just prior
to touch-down a la Soyuz?

Still, is the PICA-X heatshield up for such a thing, given SpaceX have
talked about it being reusable? Or would that call for some landing
legs to keep the shield from hitting the ground?

rick jones
--
Wisdom Teeth are impacted, people are affected by the effects of events.
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

On Jan 18, 6:28*pm, Rick Jones wrote:
Pat Flannery wrote:
Rockets mounted in the RV would serve as both a full-envelope LES, and a
vertical landing system on return, though a reserve emergency parachute
system would still be carried.
Sounds complex, but innovative:
http://spaceflightnow.com/news/n1101/18spacex/
I always thought you could use the LES as a retrorocket system if you
designed it right, but the thought of using it as a landing system never
occurred to me.

I can't imagine they are envisioning replacing chutes entirely, even
though some of that article seems to suggest it. *I mean that is a
rather decent quantity of propellant mass to do a "precise landing
under rocket power" no? Perhaps they plan on firing the LES just prior
to touch-down a la Soyuz?

Still, is the PICA-X heatshield up for such a thing, given SpaceX have
talked about it being reusable? *Or would that call for some landing
legs to keep the shield from hitting the ground?

rick jones
--
Wisdom Teeth are impacted, people are affected by the effects of events.
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

Got to give them credit they are thinking out of box

Pat Flannery writes:

Rockets mounted in the RV would serve as both a full-envelope LES, and a
vertical landing system on return, though a reserve emergency parachute
system would still be carried.
Sounds complex, but innovative:
http://spaceflightnow.com/news/n1101/18spacex/
I always thought you could use the LES as a retrorocket system if you
designed it right, but the thought of using it as a landing system never
occurred to me.

I'm still wondering what kind of engines and what amount of fuel they
want to squeeze into Dragon. The current RCS/OMS thrusters have 90
pounds of thrust each. Dragon has a mass of about 6000 kg and an LES
should be able to get the capsule away from an exploding launcher with
at least 10 g or so. This means some hefty engines which then need to
be able to throttle down deeply for a landing.

But if they can manage this: Very cool.


Jochem

--
"A designer knows he has arrived at perfection not when there is no
longer anything to add, but when there is no longer anything to take away."
- Antoine de Saint-Exupery

Rockets mounted in the RV would serve as both a full-envelope LES, and a
vertical landing system on return, though a reserve emergency parachute
system would still be carried.
Sounds complex, but innovative:
http://spaceflightnow.com/news/n1101/18spacex/
I always thought you could use the LES as a retrorocket system if you
designed it right, but the thought of using it as a landing system never
occurred to me.

Pat

On 1/18/2011 3:28 PM, Rick Jones wrote:
Pat wrote:
Rockets mounted in the RV would serve as both a full-envelope LES, and a
vertical landing system on return, though a reserve emergency parachute
system would still be carried.
Sounds complex, but innovative:
http://spaceflightnow.com/news/n1101/18spacex/
I always thought you could use the LES as a retrorocket system if you
designed it right, but the thought of using it as a landing system never
occurred to me.

I can't imagine they are envisioning replacing chutes entirely, even
though some of that article seems to suggest it. I mean that is a
rather decent quantity of propellant mass to do a "precise landing
under rocket power" no? Perhaps they plan on firing the LES just prior
to touch-down a la Soyuz?


It sounds like they are going to land it via the rockets entirely, and
only use the chutes as a back-up in case the rockets fail for some reason.
If the capsule used small extensible airbrakes to modify its descent
trajectory over the last few miles of the descent it should be able to
fall straight out of the sky at very near the aim point and not need to
do much maneuvering once the landing rockets ignite.
The Russians looked into the all-rocket braking concept for a Soyuz
succesor around the time we were designing Orion, but dropped it later:
http://www.russianspaceweb.com/soyuz_acts_history.html
The really daring Soviet design was Zarya, where it was going to land
via rockets with _no_ parachute back-up:
http://www.astronautix.com/craft/zarya.htm


Still, is the PICA-X heatshield up for such a thing, given SpaceX have
talked about it being reusable? Or would that call for some landing
legs to keep the shield from hitting the ground?


They might use blow-off or fold-down hatches in the heatshield that
would uncover deployable landing legs, like the earliest version of the
Orion CM was going to use - before they switched to airbags and then
dropped the whole concept

Pat

On 1/18/2011 5:14 PM, Jochem Huhmann wrote:

I'm still wondering what kind of engines and what amount of fuel they
want to squeeze into Dragon. The current RCS/OMS thrusters have 90
pounds of thrust each. Dragon has a mass of about 6000 kg and an LES
should be able to get the capsule away from an exploding launcher with
at least 10 g or so. This means some hefty engines which then need to
be able to throttle down deeply for a landing.

If they were using the same engines for a LES and landing, you would
think they would just add some more propellants and use them for the
retro burn also. There will probably be a minimum of four LES/landing
engines to help the descending capsule maneuver itself via varying their
thrust for final touchdown, and by firing one opposed pair as retros,
deceleration g's for the retrograde burn could be kept down to
acceptable levels.
(This is follow-up reply to the SpaceX announcement regarding they are
considering landing the manned Dragon variant via pure rocket power:
http://spaceflightnow.com/news/n1101/18spacex/ I'm cross-posting it to
sci.space.policy.)

Pat

Pat Flannery writes:

On 1/18/2011 5:14 PM, Jochem Huhmann wrote:

I'm still wondering what kind of engines and what amount of fuel they
want to squeeze into Dragon. The current RCS/OMS thrusters have 90
pounds of thrust each. Dragon has a mass of about 6000 kg and an LES
should be able to get the capsule away from an exploding launcher with
at least 10 g or so. This means some hefty engines which then need to
be able to throttle down deeply for a landing.

If they were using the same engines for a LES and landing, you would
think they would just add some more propellants and use them for the
retro burn also.

The same engines for a 10 g LES burn, for a 1 g landing and for a retro
burn which needs to be *very* precise? You'd need engines that can
throttle down to 1% or so for that.

There will probably be a minimum of four LES/landing engines to help
the descending capsule maneuver itself via varying their thrust for
final touchdown, and by firing one opposed pair as retros,
deceleration g's for the retrograde burn could be kept down to
acceptable levels.

Here's the layout of the current thrusters:

http://www.spacenews.com/images/092809Dragon02.jpg

The four downward pointing engines have a thrust of 90 pounds each. Try
to squeeze in engines with at least two orders of magnitude more
thrust and the fuel tanks for them there.

Again: Dragon has a mass of 6000 kg. To accelerate it with 10 g you'd
need engines with about 130000 lbf thrust (that's about as much as the
single Merlin engine in the first stage of Falcon 1 or the second stage
of Falcon 9). The current engines have 4 x 90 lbf.


Jochem

--
"A designer knows he has arrived at perfection not when there is no
longer anything to add, but when there is no longer anything to take away."
- Antoine de Saint-Exupery

Pat Flannery wrote:
It sounds like they are going to land it via the rockets entirely,
and only use the chutes as a back-up in case the rockets fail for
some reason.

They trying to evolve to the delta clipper/DC-X or something? Anyhow,
those backup chutes would have to be, I'm not sure what the term is,
"ballistic?" - ie ones that can be shot-out in a hurry rather than
just "released" to deal with the rocktets failing in the last few
hundred feet no?

If the capsule used small extensible airbrakes to modify its descent
trajectory over the last few miles of the descent it should be able to
fall straight out of the sky

Isn't that quite a bit of delta-V?

rick jones
--
The glass is neither half-empty nor half-full. The glass has a leak.
The real question is "Can it be patched?"
these opinions are mine, all mine; HP might not want them anyway...
feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

On 1/19/2011 2:15 AM, Jochem Huhmann wrote:


The four downward pointing engines have a thrust of 90 pounds each. Try
to squeeze in engines with at least two orders of magnitude more
thrust and the fuel tanks for them there.

Again: Dragon has a mass of 6000 kg. To accelerate it with 10 g you'd
need engines with about 130000 lbf thrust (that's about as much as the
single Merlin engine in the first stage of Falcon 1 or the second stage
of Falcon 9). The current engines have 4 x 90 lbf.

Could you do it with massed solid rockets of small size, short duration
burn time, and very high thrust?
The Dragon antitank missile use large numbers of small rocket engines to
both maintain its flight velocity and direct its course:
http://www.designation-systems.net/dusrm/m-77.html
In this scenario, you would fire all of them at once for LES, and fire
only a few at a time in sequence for landing.
I wouldn't trust landing that way, but who knows?

Pat

On 1/19/2011 10:43 AM, Rick Jones wrote:

Pat wrote:
It sounds like they are going to land it via the rockets entirely,
and only use the chutes as a back-up in case the rockets fail for
some reason.

They trying to evolve to the delta clipper/DC-X or something?


I sure hope it works better than DC-X did; that was frying its exterior
on landing from its own rocket exhaust bouncing off the ground.


Anyhow,
those backup chutes would have to be, I'm not sure what the term is,
"ballistic?" - ie ones that can be shot-out in a hurry rather than
just "released" to deal with the rocktets failing in the last few
hundred feet no?


Me, I'd go with the chutes; nothing says you can't put a steerable chute
system on it, and get landing accuracy that way.
The problem chutes run into is landing in a side-wind; at sea that's not
that bad, but on land the spacecraft can get toppled and dragged around
on its side.


If the capsule used small extensible airbrakes to modify its descent
trajectory over the last few miles of the descent it should be able to
fall straight out of the sky

Isn't that quite a bit of delta-V?


You would have to figure out its weight versus it's overall drag to find
out how fast it would be free-falling during the final stage of the
descent; as a guess, I'd say it would be easily going 300 mph or more.

Pat