Author Topic: Dream Chaser Q&A (including suggestions and improvements) (Read 663322 times)

Rocket Science · « **Reply #600 on:** 05/03/2011 05:58 pm »

I promise Chris... no need to quote me...

Rocket Science · « **Reply #601 on:** 05/03/2011 09:28 pm »

Quote from: zaitcev on 05/03/2011 03:15 pm

Quote from: HMXHMX on 05/03/2011 01:49 am
Ballistic spacecraft are at least survivable in such a contingency. Lifting bodies are less so.
Ditching is not that bad, depending on the swell. But this is another reason why Promoteus has a hatch on top.

DC will have a hatch on top.
http://www.nasaspaceflight.com/wp-content/uploads/2011/04/A315.jpg

adrianwyard · « **Reply #602 on:** 05/12/2011 12:48 am »

Re: Abort over water: ditch at high-speed, or bail out?

I've yet to find sources that say this explicitly, but as I recall you always want to bail out of the Space Shuttle in preference to a water landing. Will the same be true with Dream Chaser? The problem is at the high speeds at which the DC and Shuttle touch down (200mph+), water is very hard, and not at all smooth. As has been said earlier in this thread DC is far more boat-shaped than the Shuttle, but it's also much smaller and lighter, so waves/swells are proportionally larger and more likely to induce a tumble, so my guess is it's just as problematic for DC as for the Shuttle.

But can you easily bail out of the Dream Chaser? The hatch on top is in front of the vertical stabilizer, so you'd need a Shuttle-like extending pole to have any chance of clearing that. Moving the hatch to the side could help your chances.

There's a really convenient docking port at the back which would be an excellent place to jump out of if it could be opened easily. But I could see that adding this capability would entail undesirable compromises. Is it even wide enough to allow a pressure suited astronaut with a parachute to pass through?

I've been scouring the web for abort info on DC and come up with a discussion earlier in this thread: http://forum.nasaspaceflight.com/index.php?topic=9921.210 and: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19940030181_1994030181.pdf

Anyone know of others?

Rocket Science · « **Reply #603 on:** 05/12/2011 07:11 pm »

I have not located any tests done so far on ditching the Dream Chaser. Tests were done on the X-20 at Langley's Hydrodynamics Division. I would hope...suspect that they will do the same on DC. Bailing out wearing pressurized suits would be no easy task from the top hatch, especially with a large crew on board. It will also undergo constant CG changes during such and require corrective actions. As a pilot, "I say... if it ain't on fire, stay with the ship", ditch... then get out.
Regards
Robert

http://history.nasa.gov/SP-4308/p96a.jpg

clongton · « **Reply #604 on:** 05/12/2011 07:39 pm »

Quote from: Rocket Science on 05/12/2011 07:11 pm

I have not located any tests done so far on ditching the Dream Chaser. Tests were done on the X-20 at Langley's Hydrodynamics Division. I would hope...suspect that they will do the same on DC. Bailing out wearing pressurized suits would be no easy task from the top hatch, especially with a large crew on board. It will also undergo constant CG changes during such and require corrective actions. As a pilot, "I say... if it aint on fire, stay with the ship", ditch... then get out.
Regards
Robert

http://history.nasa.gov/SP-4308/p96a.jpg

It's always better to ditch and then get out as long as the terminal entry is under some control. It doesn't matter that the water is hard - so is a concrete runway. As long as the abort "landing" is a more or less nominal approach they should be fine (no landing gear deployed of course). After the ditch blow the top hatch and get everyone into the lift raft. If you don't do it this way the Coast Guard and the Navy will be searching hundreds of square miles of open ocean for individual crew members.

If the "landing" is at all controllable then ditch and then get out.

adrianwyard · « **Reply #605 on:** 05/12/2011 08:08 pm »

Thanks for the replies. I would like to think that ditching is the best option, but I found my source for the Shuttle: The Rogers Report.

http://history.nasa.gov/rogersrep/v1ch9.htm - Ditching section:

"Orbiter ditching was discussed by the Crew Safety Panel and at Orbiter flight techniques meetings before the first Shuttle flight. The consensus of these groups was that (1) ditching is more hazardous than suggested by the early Langley tests, and (2) ditching is probably not survivable."

Perhaps DC will have an easier time ditching than the Shuttle (there's nothing heavy in a cargo-bay to come loose, for example). I just can't help but see the thing tumbling after catching the first big-ish wave, given the speed.

Rocket Science · « **Reply #606 on:** 05/12/2011 08:17 pm »

Here are some good standard ditching techniques...
Enjoy!
http://www.pilotfriend.com/safe/safety/ditching.htm

adrianwyard · « **Reply #607 on:** 05/12/2011 08:58 pm »

Thanks for the pilotfriend link. Of course I agree there are numerous demonstrations of successful ditchings - USAir 1549 in the Hudson is a good example. As the link suggests, success is more likely with lower speeds, and smoother water (e.g. landing along swells, and not across them).

While we have to acknowledge the skill of the pilot, 1549 had the advantage of touching down at 125 knots in a river. Can DC reliably ditch traveling 50% faster than this in open ocean?

Perhaps we can agree that eventually speed, weight, strength, size/craft-shape, and the likely roughness of the water conspire to make ditching too risky to try. This is apparently the case with the Space Shuttle.

I would love to know were the DC sits on this continuum, but I think all we can do is guess at this point.

Rocket Science · « **Reply #608 on:** 05/12/2011 09:17 pm »

Yes, I agree with you all those things. We can always do buoyancy equations... A 100 ton orbiter vs an approx 10 ton DC? Look at the pic attached... no big wing to clip a wave...

http://spacecampingin.files.wordpress.com/2011/01/69757main_hl-20-fig4.gif

Hey, I say lets build some models and go find some water:)

adrianwyard · « **Reply #609 on:** 05/12/2011 10:10 pm »

Now that sounds like fun. And brings me to a second query related to its aerodynamics/shape: In all the pictures I've seen, it has no body flap. On the Shuttle, the flap also serves to protect the engine bells from the re-entry airstream.

As I understand it, the HL-20/DC shape is well-tested, and just about fixed, so I don't think it's an oversight. Do people think the bells are just resilient enough to take it?

Note: in the drop test, the aft underside of the DC has markings that presumably indicate two aerosurfaces on the rear of the body. But they lie flat, and don't extend beyond the rear.

http://www.spaceref.com/news/viewsr.html?pid=35563

baldusi · « **Reply #610 on:** 05/12/2011 10:14 pm »

There were dichting tests done. It was called BOR-4.

Rocket Science · « **Reply #611 on:** 05/12/2011 10:31 pm »

Quote from: baldusi on 05/12/2011 10:14 pm

There were dichting tests done. It was called BOR-4.

It was more of a parachute water landing than ditching... well at least it floats!
http://www.astronautix.com/craft/bor4.htm

adrianwyard · « **Reply #612 on:** 05/12/2011 11:34 pm »

Parachutes would save the day, but I worry about weight. I suppose if you forego individual parachutes and rafts for the crew that buys you some mass...

Or (and I'm ready to be shot down in flames on this one) could you deploy a small drogue chute at touch-down (ditch-down?), which will serve as an airbrake to get the speed down quickly, but is there primarily to fight against tumbling if the nose starts bouncing around on waves/swells.) It would have to be along the CG, so perhaps deployed from the base of the vertical stabilizer.

(I guess this would be handy if you came in too hot on a runway landing too.)

Rocket Science · « **Reply #613 on:** 05/13/2011 12:20 am »

Quote from: adrianwyard on 05/12/2011 11:34 pm

Parachutes would save the day, but I worry about weight. I suppose if you forego individual parachutes and rafts for the crew that buys you some mass...

Or (and I'm ready to be shot down in flames on this one) could you deploy a small drogue chute at touch-down (ditch-down?), which will serve as an airbrake to get the speed down quickly, but is there primarily to fight against tumbling if the nose starts bouncing around on waves/swells.) It would have to be along the CG, so perhaps deployed from the base of the vertical stabilizer.

(I guess this would be handy if you came in too hot on a runway landing too.)

Well If we are not going to bail out... why bring the chutes? lol I'm sure personal flotation devices, rafts are heavy and will have to calculated in. If it's not sinking, I'm sitting on top, not in the water... big fish, with big teeth!
A drouge chute for landing could come in handy like the orbiter at the base of the tail. It could have a dual mode for you application where it has it's normal mount and can shift forward to the CG mount if you like.
Using a chute near water... could catch a swell and cause more problems.
Like I said, get out the models and splash around!!
Regards
Robert

adrianwyard · « **Reply #614 on:** 05/13/2011 01:07 am »

Yes, without access to data and testing this is just dreaming. Nevertheless, whatever design has the most reasonable safety/abort modes is more likely to win in the crewed game, so it's an important thing to try and guess at.

A lifting-body like Dream Chaser has capsules beat in terms of comfort, convenience, and cross-range (for quick emergency return.) But a capsule and chutes is hard to beat for absolute survivability, ocean landing being a specific case where they diverge.

Meanwhile, anyone care to speculate why the DC's OMS engine nozzles are not protected by a body-flap or other means during re-entry? Perhaps the nozzles are replaced each flight? Also, the docking mechanism back there will definitely need protection during re-entry. A protective door, perhaps?

And another for good measure: Pictures of DC on a launch vehicle show the engines inside a fairing that blends the aeroshell with the upper stage. If the OMS is used as a LAS, shouldn't the engines be exposed? Perhaps this fairing has sections that can break away with little resistance when they fire as abort motors? But this fairing has to support a 10t vehicle for launch stresses... Wouldn't the plume reflect back off the booster if it's not directed to the sides? Enquiring minds want to know...

http://www.nasaspaceflight.com/2007/04/spacedev-announce-dream-chaser-agreement-with-ula-atlas-v/

Rocket Science · « **Reply #615 on:** 05/13/2011 09:46 pm »

Quote from: adrianwyard on 05/13/2011 01:07 am

Yes, without access to data and testing this is just dreaming. Nevertheless, whatever design has the most reasonable safety/abort modes is more likely to win in the crewed game, so it's an important thing to try and guess at.

A lifting-body like Dream Chaser has capsules beat in terms of comfort, convenience, and cross-range (for quick emergency return.) But a capsule and chutes is hard to beat for absolute survivability, ocean landing being a specific case where they diverge.
Meanwhile, anyone care to speculate why the DC's OMS engine nozzles are not protected by a body-flap or other means during re-entry? Perhaps the nozzles are replaced each flight? Also, the docking mechanism back there will definitely need protection during re-entry. A protective door, perhaps?
And another for good measure: Pictures of DC on a launch vehicle show the engines inside a fairing that blends the aeroshell with the upper stage. If the OMS is used as a LAS, shouldn't the engines be exposed? Perhaps this fairing has sections that can break away with little resistance when they fire as abort motors? But this fairing has to support a 10t vehicle for launch stresses... Wouldn't the plume reflect back off the booster if it's not directed to the sides? Enquiring minds want to know...
http://www.nasaspaceflight.com/2007/04/spacedev-announce-dream-chaser-agreement-with-ula-atlas-v/

All good questions, wish I had more students like you over the years. I would think that there is a support structure under the vehicle and that the fairing is just aero and thus a break-away clamshell. Of course this is all on spec...

Downix · « **Reply #616 on:** 05/13/2011 10:16 pm »

Quote from: adrianwyard on 05/13/2011 01:07 am

Yes, without access to data and testing this is just dreaming. Nevertheless, whatever design has the most reasonable safety/abort modes is more likely to win in the crewed game, so it's an important thing to try and guess at.

A lifting-body like Dream Chaser has capsules beat in terms of comfort, convenience, and cross-range (for quick emergency return.) But a capsule and chutes is hard to beat for absolute survivability, ocean landing being a specific case where they diverge.
Meanwhile, anyone care to speculate why the DC's OMS engine nozzles are not protected by a body-flap or other means during re-entry? Perhaps the nozzles are replaced each flight? Also, the docking mechanism back there will definitely need protection during re-entry. A protective door, perhaps?

The whole combustion chamber is replaced after each flight, based on how the SS2 runs, as they run the same engines IIRC.

Quote

And another for good measure: Pictures of DC on a launch vehicle show the engines inside a fairing that blends the aeroshell with the upper stage. If the OMS is used as a LAS, shouldn't the engines be exposed?

Not if the fairing is part of the LAS system. One of the issue of Hybrid motors is their slow firing times, compared to both liquids and solids. This can be alleviated *if* you have a fast-detonation chemical inside the combustion chamber. You don't want it there for normal ignition, however, too dangerous. But for LAS, a spray system within the fairing would be great.

As the hybrid engines run on Nitrous Oxide, the spray system would be obvious, Hydrazine. If you mix Nitrous Oxide with Hydrazine it self-ignites instantly, kicking the Hybrid engine into working order while increasing it's thrust for the first few seconds, at the cost of lifespan, which if you're in a LAS situation you don't care that much about. A simple pressure bottle within the fairing, with the nozzle pointed into the exhaust stream of each of the engines is all you'd need.

Quote

Perhaps this fairing has sections that can break away with little resistance when they fire as abort motors? But this fairing has to support a 10t vehicle for launch stresses... Wouldn't the plume reflect back off the booster if it's not directed to the sides? Enquiring minds want to know...

http://www.nasaspaceflight.com/2007/04/spacedev-announce-dream-chaser-agreement-with-ula-atlas-v/

Not if the DC is being held on with explosive bolts and gravity. If the fairing blows the bolts, and the inside has exhaust channels, the fairing could actualy be part *of* the LAS, adding an afterburner effect.

Rocket Science · « **Reply #617 on:** 05/13/2011 11:51 pm »

Hydrazine "Quick Start" I like it, might try it next winter if my car won't start...boom!! lol They are going to need something to get the detonation wave and flame propagation going in abort mode. Like to see what they come up with. IIRC Sirangelo said that he wanted the DC to be "safe" after landing, nothing toxic on board. Now if you leave the tank behind on separation...

I found some nice links on the hybrid motor, DC will be 100,000 lbs class, slide out... slide a new one in...fly away:)
Enjoy!
http://www.spaceflightnews.net/article.php?story=20040518175050117
http://airbum.com/pireps/PirepSS1.html

Downix · « **Reply #618 on:** 05/14/2011 01:44 am »

Quote from: Rocket Science on 05/13/2011 11:51 pm

Hydrazine "Quick Start" I like it, might try it next winter if my car won't start...boom!! lol They are going to need something to get the detonation wave and flame propagation going in abort mode. Like to see what they come up with. IIRC Sirangelo said that he wanted the DC to be "safe" after landing, nothing toxic on board. Now if you leave the tank behind on separation...

I found some nice links on the hybrid motor, DC will be 100,000 lbs class, slide out... slide a new one in...fly away:)
Enjoy!
http://www.spaceflightnews.net/article.php?story=20040518175050117
http://airbum.com/pireps/PirepSS1.html

As I said, in the interstage. Left behind.

Lars_J · « **Reply #619 on:** 05/14/2011 05:27 am »

About ditching using the Dreamchaser - given that the DC is comparable in mass to the capsules, would it not make more sense to have a parachute (for the entire DC) for situations where you have to ditch in the ocean or you are unable to reach a runway. It would add mass but might be worth it. Just like crew in commercial capsules are not expected to wear personal parachutes, the same could apply for the DC.