Author Topic: SNC outline Dream Chaser's Enterprise-style landing test approach  (Read 35382 times)

Offline Rocket Science

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Lifting Body Air and Spacecraft Q & A

With 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


May 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.
Done, Thanks Tom! :)
"The laws of physics are unforgiving"
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Offline TomH

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It 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


Are 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.
« Last Edit: 06/10/2012 01:05 AM by TomH »

Offline spectre9

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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.

Offline Lurker Steve

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It 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


Are 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 read the NASA report, and it said the blow-out was in the main gear. I'm not sure why they would change the nose wheel when that's not where the problem occurred.

It sounds like the solution was thicker tires and a smoother runway surface. Add in the parachutes also.

How much speed did the shuttle have during landings ? I think the DreamChaser will actually come in a bit slower, right ? Less airspeed means less braking on the runway.

Offline jnc

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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.

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
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Offline Jim

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It 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.
« Last Edit: 06/10/2012 02:16 AM by Jim »

Offline Zachstar

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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.

ANY ability to go outside ISS 6 month stays has no bearing on the selection process. That would at once cause one hell of an uproar. The contract is for crew flights to the ISS. That is it.

Edit2: What it really has as a trump card is how different it is from the SpaceX and from the capsule concept itself. Thus it becomes a very effective backup to SpaceX. Tho congress will balk at this because they think companies like SN are the next Solyndra waiting to happen. They will want old big bloated company involvement and Boeing fits this #2 perfectly.
« Last Edit: 06/10/2012 04:09 AM by Zachstar »

Offline TomH

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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.

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


I'd say you interpreted it correctly. I have to wonder, however, if the initial design, in an attempt toward minimal mass, made the landing system not enough robust.

Offline BrightLight

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One of the advantages that SNC holds is that it is a very large contractor in the defense industry, and as such has deep resources to  use for development and manufacturing. The development and manufacturing of DC should be easily managed by SNC, they have the depth and breath to build sub systems internally and the management skills to run the contracts with Boeing etc. It appears from there first full scale flight test that they are rapidly running up the learning curve in flying and testing new airframes.  I hope they can make it thru to orbital tests.

Offline TomH

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It 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.


LOL, Thanks Jim.  What mass penalty was incurred? I presume the changes involved hydraulics, not fly by wire with electric motors?  It sounds like there were multiple factors involved. I would think DC has such a lighter mass than STS that the braking and steering systems could be considerably different. Obviously, a front skid is not going to have the steering agility of a steerable nose wheel.

Offline TomH

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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.

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.

Offline jnc

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Active 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
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(old bumper sticker)

Offline Rocket Science

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Active 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... ;)

http://forum.nasaspaceflight.com/index.php?topic=9921.msg878422#msg878422
"The laws of physics are unforgiving"
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Offline jnc

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We discussed this before, have a look... ;)

Hmmm - the NASA page that discussion links to (here) seems initially to contradict the other page on this point - and then winds up potentially contradicting itself!

"until nose wheel steering and improved brakes were installed" (implying it didn't have NWS before)

and then:

"The space planes have been outfitted with ... additional nose wheel steering capability."

Now, whether to read that latter as 'there was some there before and we added to it' (which is how one would normally read that, I think) or 'we added an additional capability' - who knows?

What troubles me is that the other NASA page said that before the blowout, "because the nose gear had only a single strain control system, shuttle pilots were reluctant to use it at all, preferring differential braking .. to control the shuttle's rollout down the runway", that did seem to imply pretty forcefully that they had a choice of two systems, and preferred the differential braking - so what was the other choice, then, if not NWS?

I'm just going to throw up my hands at this point! :)

Noel
"America Needs - Space to Grow"

(old bumper sticker)

Offline zerm

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Regarding nose wheel steering, most ground steering (particularly during landing) on any aircraft is done by differential braking to starboard and port wheels.

The above statement is completely incorrect. On aircraft with weights below 12,500 ground steering is done by way of breaks- but only at low speeds. On aircraft over 12,500 a tiller is used to rotate the nose wheel for steering. "During landing" ALL aircraft use aerodynamic surfaces until dropping below an airspeed directed by the aircraft's manual. Once reaching such a speed aircraft below 12,500# will use breaking to steer, aircraft over 12,500 will use the tiller. Although large aircraft (over 12,500#) have the ability to use differential braking, it is not normally done as it can cause problems in the breaking system, it's not fun for the passengers, provides wear and tare and is less precise than using the tiller.

I'm an ATP, Captain under FAR 121 and have flown both light and heavy aircraft of many sorts from airliners to corporate jets to bug smashers over the past 35 years. Plus I have a  Degree in Aeronautical Science. Thus, you all can take what I say here FWIW.
« Last Edit: 06/11/2012 01:22 AM by zerm »

Offline spectre9

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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.

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.

It would be good to be able to examine those that have had a 500 day in space before subjecting those astronauts to the high g loads of a BEO reentry. Possibly by throwing these people into ground based experiments to see if they would've handled a full Orion landing in their weakened state.

I know it isn't part of the currrent ISS mission but that might be a problem. The ISS mission has not been clearly defined here. As it currently is there will only be small crews on 6 month rotation and NOT PAST 2020. I'm sure this will change especially with international partners calling for greater ISS utilisation working towards exploration of deep space.

Offline Zachstar

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That has nothing to do with the Dream Chaser. Can we focus on the topic at hand?

Offline spectre9

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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.

Offline Zachstar

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It can't be used as an advantage because that is not part of the selection process. The extra time it can stay in orbit as with the others is good in case of urgent need to hold off return. Its method of return is relevant because NASA wants options for return. (Water, Land, Crossrange, Emergency Options)

"Soft Landings" are not part of it. And anyone using any craft has to be able to withstand a hard landing anyway in case of survivable failure. It would be completely unethical otherwise.

Offline A_M_Swallow

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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.

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.

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