Great article - I look forward to seeing this bird fly.
How long will the ALT test program last.How fast will the DC go with its rocketsHow high will she get.
Quote from: BrightLight on 06/09/2012 02:50 pmHow long will the ALT test program last.How fast will the DC go with its rocketsHow high will she get.I asked all those questions. For the first, they weren't sure because it would depend on how things went, sort of like SpaceX and C2/C3/C2+. For the second two, they weren't ready to share that information yet, but they did point out that the engines are quite powerful and so they could expand the envelope significantly compared to a free drop.
http://www.nasaspaceflight.com/2012/06/snc-dream-chasers-enterprise-test-approach/Really, really enjoying writing these up. Again thanks to Lee Jay for carrying out the interview for this latest series of content (full resources in L2).Another article to come in this series.
What exactly is the challenge with tires in space ? I assume they aren't inflatable tires, but one solid piece of rubber-like material. I can understand the issues with handling a gas-filled tire in space. Too much expansion / contraction with the pressure changes. Is the problem with a "steer-able" wheel, where the steering mechanism might freeze up , and that doesn't happen with the rear wheels that are only expected to roll in a fixed direction ?
Quote from: Lurker Steve on 06/09/2012 03:19 pmWhat exactly is the challenge with tires in space ? I assume they aren't inflatable tires, but one solid piece of rubber-like material. I can understand the issues with handling a gas-filled tire in space. Too much expansion / contraction with the pressure changes. Is the problem with a "steer-able" wheel, where the steering mechanism might freeze up , and that doesn't happen with the rear wheels that are only expected to roll in a fixed direction ?Given the thermal environment and ranges it sees the tire pressures have to monitored appropriately. In addition, in order to keep the tires healthy this could be a driver from a thermal perspective. And given this vehicle projected length of stay on orbit it is easier if one tire can be removed, especially when it is in a different zone of the vehicle.
Quote from: Go4TLI on 06/09/2012 03:26 pmQuote from: Lurker Steve on 06/09/2012 03:19 pmWhat exactly is the challenge with tires in space ? I assume they aren't inflatable tires, but one solid piece of rubber-like material. I can understand the issues with handling a gas-filled tire in space. Too much expansion / contraction with the pressure changes. Is the problem with a "steer-able" wheel, where the steering mechanism might freeze up , and that doesn't happen with the rear wheels that are only expected to roll in a fixed direction ?Given the thermal environment and ranges it sees the tire pressures have to monitored appropriately. In addition, in order to keep the tires healthy this could be a driver from a thermal perspective. And given this vehicle projected length of stay on orbit it is easier if one tire can be removed, especially when it is in a different zone of the vehicle.I understand there may be a challenge there, but hasn't that already been tested in the X-37? Does it have a nose skid or a tire?
What exactly is the challenge with tires in space ? I assume they aren't inflatable tires, but one solid piece of rubber-like material.
Thanks Lee Jay. FWIW - you are a generous person, thanks again.
It's good that we're getting some quality reports on Dreamchaser; thanks Chris and Lee Jay.Is White Knight II the only fixed wing mothership available? SCA is the only other option I can think of.
Is White Knight II the only fixed wing mothership available? SCA is the only other option I can think of.
Quote from: arachnitect on 06/09/2012 04:09 pmIs White Knight II the only fixed wing mothership available? SCA is the only other option I can think of.Orbital's L-1011?
It seems like the WKII or a B-52 are the only options for a simpler drop (compared to being carried on top). But it might be too much even for a B-52?
Regarding nose wheel steering, most ground steering (particularly during landing) on any aircraft is done by differential braking to starboard and port wheels.
Not sure if the causes for the Shuttle's issues would carryover to DC, though.Noel
Quote from: TomH on 06/09/2012 07:35 pmRegarding nose wheel steering, most ground steering (particularly during landing) on any aircraft is done by differential braking to starboard and port wheels.Yes, but the Shuttle had both differential braking and steerable nosewheels, and after 'issues' (a blowout) they started using the latter more. (More here.) Not sure if the causes for the Shuttle's issues would carryover to DC, though.Noel
Quote from: Rocket Science on 06/10/2012 12:27 amLifting Body Air and Spacecraft Q & AWith all the interest generated by Dream Chaser and its direct ancestor the HL-20 and all the other lifting body vehicles, I created this thread to discuss, inform and exchange general questions, ideas and answers as to what exactly a Lifting Body is. This is to keep the Dream Chaser threads clean and without clutter and OT topics as things get busier now. http://forum.nasaspaceflight.com/index.php?topic=29126.msg914401;topicseen#newO.K., you are not being clear enough in whatever you are trying to imply and what you want us to infer. You state here that the thread was "created to discuss...what exactly a lifting body is." In the same sentence you include "...discuss, inform, and exchange general questions..." The thread title clearly references "...landing test..."Are you saying that brakes and steering are not part of landing? Are you saying that because you started the thread you feel the prerogative strictly to control the posts if they do not meet your definition of being on-topic or off-topic? Just asking, because I want to understand you with complete clarity before I respond further.
Lifting Body Air and Spacecraft Q & AWith all the interest generated by Dream Chaser and its direct ancestor the HL-20 and all the other lifting body vehicles, I created this thread to discuss, inform and exchange general questions, ideas and answers as to what exactly a Lifting Body is. This is to keep the Dream Chaser threads clean and without clutter and OT topics as things get busier now. http://forum.nasaspaceflight.com/index.php?topic=29126.msg914401;topicseen#new
It is a stretch for me to believe that use of port and starboard brakes to steer caused any problem on STS.
Quote from: Rocket Science on 06/10/2012 12:27 amLifting Body Air and Spacecraft Q & AWith all the interest generated by Dream Chaser and its direct ancestor the HL-20 and all the other lifting body vehicles, I created this thread to discuss, inform and exchange general questions, ideas and answers as to what exactly a Lifting Body is. This is to keep the Dream Chaser threads clean and without clutter and OT topics as things get busier now. http://forum.nasaspaceflight.com/index.php?topic=29126.msg914401;topicseen#newMay I suggest you change this thread to say the thread linked below? Chris created this thread and at first read it sounded like you were chastising us for posts we have made immediately above. I had figured out what you meant and deleted the post you quoted before you finished your reply.
Quote from: TomH on 06/10/2012 12:23 amIt is a stretch for me to believe that use of port and starboard brakes to steer caused any problem on STS. Hey, I'm just passing on what that NASA web site I linked to said - take it up with them.Noel
Quote from: jnc on 06/10/2012 12:53 amQuote from: TomH on 06/10/2012 12:23 amIt is a stretch for me to believe that use of port and starboard brakes to steer caused any problem on STS. Hey, I'm just passing on what that NASA web site I linked to said - take it up with them.NoelAre you sure you read it all correctly and did you read and understand the entirity of my post above? I am not certain, but I wonder if the changes involved making the nose wheel able to free pivot or making it actively steerable from the stick. There is a huge difference. Taking a non-steerable wheel and making it steerable would involve a lot of hydraulic re-plumbing as well as add excessive weight, an ability and mass that are completely unnecessary. You posted it; I'm not "taking it up with you" so to speak, but rather discussing a concept that you introduced.
I wonder if the changes involved making the nose wheel able to free pivot or making it actively steerable from the stick. There is a huge difference.
I hope the landings are nice and smooth.This is the ace Dream Chaser holds.After long duration Mars simulations on orbit astronauts might need a comfortable touchdown and getting the right medical staff and other support crews to a remote locations / splashdown sites could prove costly in the long run.I like that SNC works with Boeing, don't know exactly how. Something to do with the flight controls and simulator?The stuff with the university students didn't go unnoticed either.I think the good will that's been generated in such a short time really increases the chances of Dream Chaser becoming a reality.Can't wait to see free flight and landing.This is the big intangible draw card DC has. It will be a poster child. Something to put in the presentations and show to the public. Surely we've all heard the "capsules are boring" lines from those less enthused by the space program. Any support that NASA can get is worth going for.
Quote from: TomH on 06/10/2012 01:01 amI wonder if the changes involved making the nose wheel able to free pivot or making it actively steerable from the stick. There is a huge difference.From the NASA page:"because the nose gear had only a single strain control system, shuttle pilots were reluctant to use it at all, preferring differential braking with the main landing gear instead to control the shuttle's rollout down the runway"[Then, after the failure and subsequent investigations...]"The nose wheel was given greater steering authority" (emphasis mine)So, how would you interpret those statements?Noel
Quote from: TomH on 06/10/2012 12:23 amIt is a stretch for me to believe that use of port and starboard brakes to steer caused any problem on STS. It doesn't matter what you believe, differential braking was part of the problems with the brake system, along with orbiter weight growth and axle flexing. Active nose wheel steering was added.
This is the ace Dream Chaser holds.After long duration Mars simulations on orbit astronauts might need a comfortable touchdown and getting the right medical staff and other support crews to a remote locations / splashdown sites could prove costly in the long run.
Active nose wheel steering was added.
Quote from: Jim on 06/10/2012 02:13 amActive nose wheel steering was added.Is that 'nose-wheel steering, previously not present, was added', or 'extra authority was added to that already present'? I ask because the more natural reading of that is the first, but that page I quoted (upthread) said a couple of things (e.g. "nose wheel was given greater steering authority") which imply (to me) that there was some there to start with?Noel
We discussed this before, have a look...
Quote from: spectre9 on 06/10/2012 01:30 amThis is the ace Dream Chaser holds.After long duration Mars simulations on orbit astronauts might need a comfortable touchdown and getting the right medical staff and other support crews to a remote locations / splashdown sites could prove costly in the long run.Wouldn't an actual Mars return likely hold the possibility of an even more difficult return? Fatigue, possible injuries sustained on the Martian surface. DC would not be available then, only Orion (possibly an advanced Dragon). AFAIK, DC's TPS cannot dissipate any heat greater than that generated by LEO return. I would think it better to practice long duration returns in the same craft that will actually be used on a real Mars return.
Is the mission for Dream Chaser in any way not tied into the ISS?Off topic to discuss it's one and only destination? C'mon mate, leave it to the mods.If the soft landings provided by DC can't be applied to the ISS mission that feature can't be used as an advantage over the competition.This needs to be defined.
Quote from: spectre9 on 06/11/2012 09:05 amIs the mission for Dream Chaser in any way not tied into the ISS?Off topic to discuss it's one and only destination? C'mon mate, leave it to the mods.If the soft landings provided by DC can't be applied to the ISS mission that feature can't be used as an advantage over the competition.This needs to be defined.The Dream Chaser may be able to fly to a Bigelow spacestation as well as the ISS. Although Mr Bigelow may want it to take off on both Atlas V and Falcon 9 launch vehicles.To go to an EML-1/2 spacestation the Dream Chaser would need a kicker/upper stage with a delta-V of 3.77 km/s. Unless the thermal protection system has been upgraded then the upper stage will need an addition delta-V of 3.77 km/s to bring the spacecraft back to LEO.I am assuming that the Dream Chaser can carry sufficient food, water and ECLSS for the return journey.
DC will not be flying BEO. An extra 3.77 km/s is unbearable.
Quote from: Jason1701 on 06/12/2012 07:34 amDC will not be flying BEO. An extra 3.77 km/s is unbearable.You may have used the wrong word there. 3.77 km/s is bearable in the Orion or Dragon but not in the Dream Chaser(?).
Quote from: A_M_Swallow on 06/12/2012 07:25 pmQuote from: Jason1701 on 06/12/2012 07:34 amDC will not be flying BEO. An extra 3.77 km/s is unbearable.You may have used the wrong word there. 3.77 km/s is bearable in the Orion or Dragon but not in the Dream Chaser(?).Exactly right. It has to do with TPS constraints, partly. Ablative can handle (at the extreme end, like the Galileo probe and nuclear warheads penetrating deep in the atmosphere at hypersonic velocities) almost arbitrary reentry heat loads, while tiles like the Shuttle or Dream Chaser use are only suitable for certain heat loads. The Shuttle/DreamChaser/X37B has to fly a very precise high-lifting reentry corridor or the TPS will fail.
Quote from: Jason1701 on 06/12/2012 07:34 amDC will not be flying BEO. An extra 3.77 km/s is unbearable.You may have used the wrong word there. 3.77 km/s is bearable in the Orion or Dragon but not in the Dream Chaser(?).p.s. I was planning on using thrust to return to LEO so the heat shield would only get a similar amount of heat. Unfortunately the inspace stage will need enormous propellant tanks (2 * 3.77 = 7.54 km/s)
Quote from: A_M_Swallow on 06/12/2012 07:25 pmQuote from: Jason1701 on 06/12/2012 07:34 amDC will not be flying BEO. An extra 3.77 km/s is unbearable.You may have used the wrong word there. 3.77 km/s is bearable in the Orion or Dragon but not in the Dream Chaser(?).p.s. I was planning on using thrust to return to LEO so the heat shield would only get a similar amount of heat. Unfortunately the inspace stage will need enormous propellant tanks (2 * 3.77 = 7.54 km/s)I meant that the 3.77 km/s to return to LEO is an unbearable addition to the delta-v budget. As you said, it would mean DC would be like a SSTO. Returning to LEO propulsively just so you can reenter is goofy.
Quote from: Jason1701 on 06/13/2012 01:04 amQuote from: A_M_Swallow on 06/12/2012 07:25 pmQuote from: Jason1701 on 06/12/2012 07:34 amDC will not be flying BEO. An extra 3.77 km/s is unbearable.You may have used the wrong word there. 3.77 km/s is bearable in the Orion or Dragon but not in the Dream Chaser(?).p.s. I was planning on using thrust to return to LEO so the heat shield would only get a similar amount of heat. Unfortunately the inspace stage will need enormous propellant tanks (2 * 3.77 = 7.54 km/s)I meant that the 3.77 km/s to return to LEO is an unbearable addition to the delta-v budget. As you said, it would mean DC would be like a SSTO. Returning to LEO propulsively just so you can reenter is goofy.Not everything has to go to both LEO and beyond LEO.
We agree. And Dream Chaser should clearly just to go LEO, rather than become a SSTO to go beyond.
Quote from: Jason1701 on 06/13/2012 01:12 amWe agree. And Dream Chaser should clearly just to go LEO, rather than become a SSTO to go beyond.DC was never a Single Stage To Orbit vehicle.
Quote from: Go4TLI on 06/13/2012 01:18 amQuote from: Jason1701 on 06/13/2012 01:12 amWe agree. And Dream Chaser should clearly just to go LEO, rather than become a SSTO to go beyond.DC was never a Single Stage To Orbit vehicle. But it would need the mass ratio of one to fulfill Swallow's propulsive-braking-to-LEO idea.
There is a significant difference. SSTO have a delta-V of 9.3 -10 km/s.The inspace stage(s) would need a delta-v of ~7.54 km/s.
Quote from: A_M_Swallow on 06/13/2012 03:20 amThere is a significant difference. SSTO have a delta-V of 9.3 -10 km/s.The inspace stage(s) would need a delta-v of ~7.54 km/s.Still a lot of delta-V. Facts are:DreamChaser cannot perform direct reentry from Lunar/EML-2Propulsive deorbit is not a reasonable solutionTherefore, DreamChaser will not fly BEOHowever, ISS is the only guaranteed destination for the foreseeable future, and none of the commercial vehicles will be going BEO anyway without modification.
What exactly is the challenge with tires in space ? I assume they aren't inflatable tires, but one solid piece of rubber-like material. I can understand the issues with handling a gas-filled tire in space. Too much expansion / contraction with the pressure changes.
Quote from: Lurker Steve on 06/09/2012 03:19 pmWhat exactly is the challenge with tires in space ? I assume they aren't inflatable tires, but one solid piece of rubber-like material. I can understand the issues with handling a gas-filled tire in space. Too much expansion / contraction with the pressure changes. I had a chance to spend some time with one of the Shuttle tire engineers. They felt the environment for the tires in space was fairly benign. They were inflated with nitrogen at 315psi, a somewhat higher pressure than used on a airliner, but they were essentially normal 737-type aircraft tires and cost only about $5K apiece, which was minimal for Shuttle hardware. The temperature range in orbit was not excessive for tires.
What about solid rubber-like tires?
This is space, not aircraft. Don't need inflated tires.Time to think about a paradigm change - wire spring tires.
Quote from: vulture4 on 07/15/2012 05:01 pmQuote from: Lurker Steve on 06/09/2012 03:19 pmWhat exactly is the challenge with tires in space ? I assume they aren't inflatable tires, but one solid piece of rubber-like material. I can understand the issues with handling a gas-filled tire in space. Too much expansion / contraction with the pressure changes. I had a chance to spend some time with one of the Shuttle tire engineers. They felt the environment for the tires in space was fairly benign. They were inflated with nitrogen at 315psi, a somewhat higher pressure than used on a airliner, but they were essentially normal 737-type aircraft tires and cost only about $5K apiece, which was minimal for Shuttle hardware. The temperature range in orbit was not excessive for tires.This is not entirely accurate. Tires are an item that must be managed in space. Not only will they slowly leak over time (just as the tires on your vehicle do) but the thermal environments must be managed to the point that the pressures do not climb to high or drop too low.This is much easier to accomplish with a free-flying vehicle than it is with a vehicle docked to a station where now there very well can be (and are) competing systems for various environments and working the issues as an integrated stack.
Quote from: clongton on 07/16/2012 05:25 pmThis is space, not aircraft. Don't need inflated tires.Time to think about a paradigm change - wire spring tires.No, this part is very much aircraft.It is not the moon.Can't take the spinup and scuffing from landing.
Don't forget also that this vehicle is designed for 210 docked days - a heck of a lot longer than Shuttle.
Can't take the spinup and scuffing from landing.
Quote from: Jim on 07/16/2012 11:35 pmCan't take the spinup and scuffing from landing.Simple. Armature built into the hub. Just before touchdown, spin it up to landing speed. Automatically initiated by ground proximity.Thinking outside the box.
Shuttle’s nose gear tires might be correctly sized for DC’s main gear and are already space qualified. Perhaps stocks are still available…
Quote from: Rocket Science on 07/17/2012 12:36 amShuttle’s nose gear tires might be correctly sized for DC’s main gear and are already space qualified. Perhaps stocks are still available…Yes but DC is supposed to stay in space for 10x longer than Shuttle - can the Shuttle nose gear handle that? (references for or against would be welcome)
Quote from: clongton on 07/17/2012 02:06 amQuote from: Jim on 07/16/2012 11:35 pmCan't take the spinup and scuffing from landing.Simple. Armature built into the hub. Just before touchdown, spin it up to landing speed. Automatically initiated by ground proximity.Thinking outside the box.You think wings are useless in space?
Quote from: Jim on 07/17/2012 02:17 amQuote from: clongton on 07/17/2012 02:06 amQuote from: Jim on 07/16/2012 11:35 pmCan't take the spinup and scuffing from landing.Simple. Armature built into the hub. Just before touchdown, spin it up to landing speed. Automatically initiated by ground proximity.Thinking outside the box.You think wings are useless in space? I do.
Quote from: clongton on 07/17/2012 01:51 pmQuote from: Jim on 07/17/2012 02:17 amYou think wings are useless in space? I do.But, eventually the space craft enters the atmosphere, and those wings have a purpose again. Even a capsule's heatshield is useless in space, but you have to carry some extra weight around if you plan on re-entry.
Quote from: Jim on 07/17/2012 02:17 amYou think wings are useless in space? I do.
You think wings are useless in space?
Quote from: clongton on 07/17/2012 02:06 amQuote from: Jim on 07/16/2012 11:35 pmCan't take the spinup and scuffing from landing.Simple. Armature built into the hub. Just before touchdown, spin it up to landing speed. Automatically initiated by ground proximity.Thinking outside the box.KISS = regular tires and nose skid, just as SNC has done. No fancy, custom solution that adds on to cost and complexity needed.Edit : Spaceshipone used same config.
Quote from: clongton on 07/17/2012 01:51 pmQuote from: Jim on 07/17/2012 02:17 amQuote from: clongton on 07/17/2012 02:06 amQuote from: Jim on 07/16/2012 11:35 pmCan't take the spinup and scuffing from landing.Simple. Armature built into the hub. Just before touchdown, spin it up to landing speed. Automatically initiated by ground proximity.Thinking outside the box.You think wings are useless in space? I do.They are useful for catching orbital debris and micrometeors on the TPS.;-)
Err... lifting bodies have more internal volume, they are "fatter". The Shuttle had wings because of cross range consideration. Read the history of the discussions.
The environment for the Shuttle tires (conventional aircraft tires inflated with nitrogen) was considered fairly benign. The X-37 uses smaller but otherwise similar tires with 300psi inflation pressure. It had one tire blowout on the first landing but otherwise no problems. Regarding wings, I realize people have their preferences and aerodynamics may not generate a lot of interest. But the X-37 wings provide a much higher lift to drag ratio than the Dreamchaser's wingless lifting body shape and because it depends much less on body lift the X-37 can utilize a more efficient fuselage shape, with more internal volume, less structural mass, and less internal stress when pressurized. In fact this is why after decades of work with lifting bodies NASA decided to use wings for the Shuttle. However I think the X-37 has a significant advantage over either the DC or Shuttle because of the long moment arm between its V-tail surfaces and the center of pressure, giving it greater tolerance for CG location (always a concern with the Shuttle) and much better pitch control when landing in variable or suboptimal winds, which often present themselves.The question of wings vs parachute for landing is not a matter of mass, but of cost. A winged vehicle is easier to make fully reusable because there is no need for portions of the vehicle to be dropped (i.e. the heatshield for the CST) or deployed and refurbished, like the parachutes. The actual energy (i.e. fuel) to lift the wings into space costs almost nothing, and the X-37 of course had no foam fragments to damage its thermal tiles. For a given booster lift capacity, a capsule will have more payload mass and volume than a runway lander, so as long as the booster is thrown away the capsule will have a cost or payload advantage. But if and when fully reusable boosters are available the initial booster cost will have little impact and one can simply choose a slightly larger booster. The easier reuse of the runway lander will then be a significant advantage.
The environment for the Shuttle tires (conventional aircraft tires inflated with nitrogen) was considered fairly benign.
Regarding wings, I realize people have their preferences and aerodynamics may not generate a lot of interest. But the X-37 wings provide a much higher lift to drag ratio than the Dreamchaser's wingless lifting body shape
and because it depends much less on body lift the X-37 can utilize a more efficient fuselage shape, with more internal volume, less structural mass, and less internal stress when pressurized.
In fact this is why after decades of work with lifting bodies NASA decided to use wings for the Shuttle.
However I think the X-37 has a significant advantage over either the DC or Shuttle because of the long moment arm between its V-tail surfaces and the center of pressure, giving it greater tolerance for CG location (always a concern with the Shuttle) and much better pitch control when landing in variable or suboptimal winds, which often present themselves.
The question of wings vs parachute for landing is not a matter of mass, but of cost.
A winged vehicle is easier to make fully reusable because there is no need for portions of the vehicle to be dropped (i.e. the heatshield for the CST) or deployed and refurbished, like the parachutes.
The actual energy (i.e. fuel) to lift the wings into space costs almost nothing, and the X-37 of course had no foam fragments to damage its thermal tiles.
For a given booster lift capacity, a capsule will have more payload mass and volume than a runway lander, so as long as the booster is thrown away the capsule will have a cost or payload advantage. But if and when fully reusable boosters are available the initial booster cost will have little impact and one can simply choose a slightly larger booster. The easier reuse of the runway lander will then be a significant advantage.
Wings versus parafoil is absolutely a matter of mass. A large portion of an aircraft's mass lies in the wings, especially one that's supersonic (or hypersonic). The main spar is quite heavy, and the control mechanisms aren't light either. The gear gets heavy when the high-speed landing is figured in, and the main spar gets heavier with the heavy gear. If the wing is wet, not the case here, the spar gets even more massive, not to mention the weight of the tanks. The X-38's parafoil was very much a way to achieve a lower stall with less mass.Max Hunter's observation was that the wings were such a major portion of a spacecraft's weight that by leaving the wings off, one could carry so much extra propellant that vertical landing was possible.QuoteA winged vehicle is easier to make fully reusable because there is no need for portions of the vehicle to be dropped (i.e. the heatshield for the CST) or deployed and refurbished, like the parachutes. Here again that's the opposite of what's true. A single center of forward pressure is far simpler to protect than a collection of leading edges and a belly, along with the gear and tires. That's why capsules really are easier.