Author Topic: SNC building test schedule for Dream Chaser – Dryden Drop Tests upcoming  (Read 42038 times)

Offline Jim

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Jim, a question... Cannot SNC fit whatever sized nozzle to which ever part of the flight envelope they wish to test? It is a bolt-on operation...

Most nozzles for composite SRM's aren't bolt-on

Offline Rocket Science

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Jim, a question... Cannot SNC fit whatever sized nozzle to which ever part of the flight envelope they wish to test? It is a bolt-on operation...

Most nozzles for composite SRM's aren't bolt-on
Yea Jim you are right . ;) I was thinking about the bolts around the circumference on the end case on the ground test motors.  The motors are one piece composite. In that case they would have to produce motors with different optimized nozzles....

Edit to add:

Thinking about this a bit more... DC would have to be able to perform a Pad Abort using standard ops motors and nozzles. So why can’t a single nozzle design be used for the test flights as well?
« Last Edit: 12/30/2012 02:49 PM by Rocket Science »
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Offline adrianwyard

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And isn't CST-100 using RS-88 for both abort (from sea level presumably) and orbital maneuvering, i.e. vacuum?

Offline joek

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And isn't CST-100 using RS-88 for both abort (from sea level presumably) and orbital maneuvering, i.e. vacuum?

Only tenuously related to RS-88 AFAICT.  CST-100 abort motors are Bantam-derived but are pressure-fed hypergolic ablative.  No idea if they're intended for orbital maneuvering, although Boeing has made noises about them being potentially used for ISS reboost.

Online Patchouli

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Jim, a question... Cannot SNC fit whatever sized nozzle to which ever part of the flight envelope they wish to test? It is a bolt-on operation...

Most nozzles for composite SRM's aren't bolt-on
Yea Jim you are right . ;) I was thinking about the bolts around the circumference on the end case on the ground test motors.  The motors are one piece composite. In that case they would have to produce motors with different optimized nozzles....

Edit to add:

Thinking about this a bit more... DC would have to be able to perform a Pad Abort using standard ops motors and nozzles. So why can’t a single nozzle design be used for the test flights as well?

The most obvious solution would be to run a nozzle that is a compromise between what's needed for vacuum and sea level like what was done on the SSME.

You loose some ISP but it likely would be lighter and simpler then using an articulated nozzle extension or aerospike.

The Atlas V is doing most of the work getting to orbit and it's an orbital vehicle so you can afford to have a less then optimal ISP.
« Last Edit: 12/31/2012 02:50 AM by Patchouli »

Offline Lee Jay

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In a DC thread some time ago people expressed doubt that one nozzle design could be chosen that would work in vacuum and the atmosphere. I'm not sure if this is in fact that big a problem (shuttle SRM nozzle operated from 0-146K ft without trouble) but if it is, then the hybrids couldn't be used for drop tests

I asked them specifically if the hybrids would be used for the drop tests, and Mark Sirangelo said that they would be.  I think it's reasonable to assume that he knows what he's talking about given that he's former CEO of Spacedev and current head of SNC Space Systems.

This was in the context of high altitude releases from carrier aircraft, not from the helicopter.

Online Patchouli

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I wonder if the best option would be to pull the NASA B-52s out of retirement.

Offline Rocket Science

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In a DC thread some time ago people expressed doubt that one nozzle design could be chosen that would work in vacuum and the atmosphere. I'm not sure if this is in fact that big a problem (shuttle SRM nozzle operated from 0-146K ft without trouble) but if it is, then the hybrids couldn't be used for drop tests

I asked them specifically if the hybrids would be used for the drop tests, and Mark Sirangelo said that they would be.  I think it's reasonable to assume that he knows what he's talking about given that he's former CEO of Spacedev and current head of SNC Space Systems.

This was in the context of high altitude releases from carrier aircraft, not from the helicopter.
Exactly Lee Jay, I remember that and that is one of the reasons that I fail to understand the concern over it. The only difference that it would be done later in the test flights as Mark stated. Circumstances have changed and perhaps other options made need to be examined including boost to climb sooner rather than later...
« Last Edit: 12/31/2012 12:21 PM by Rocket Science »
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Offline Lee Jay

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In a DC thread some time ago people expressed doubt that one nozzle design could be chosen that would work in vacuum and the atmosphere. I'm not sure if this is in fact that big a problem (shuttle SRM nozzle operated from 0-146K ft without trouble) but if it is, then the hybrids couldn't be used for drop tests

I asked them specifically if the hybrids would be used for the drop tests, and Mark Sirangelo said that they would be.  I think it's reasonable to assume that he knows what he's talking about given that he's former CEO of Spacedev and current head of SNC Space Systems.

This was in the context of high altitude releases from carrier aircraft, not from the helicopter.
Exactly Lee Jay, I remember that and that is one of the reasons that I fail to understand the concern over it. The only difference that it would be done later in the test flights as Mark stated. Circumstances have changed and perhaps other options made need to be examined including boost to climb sooner rather than later...

You know, as usual, Chris is on top of it.  It says this in his article:

http://www.nasaspaceflight.com/2012/06/snc-dream-chasers-enterprise-test-approach/

"“We want to expand the envelope up, starting low, and gradually  increasing in altitude, speed and maneuvers,” added Mr Sirangelo. “It’s  going to have some forward momentum (with the helicopter) as we’re  moving it and then it’s going to drop very quickly, then it’ll pick up  speed and then it’ll pick up lift and then it’ll fly in and do its  work.” The test plan also progresses towards the use of Dream Chaser’s  hybrid motors, for the purpose of expanding the flight envelope to  be both faster and higher, during the later stages of testing."
I'm not sure why there's a question about this.

Offline adrianwyard

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If the RCS can also operate at all altitudes,


No such thing.

Do you say this because it's not possible to design one nozzle that's optimized for all ambient pressures? Or for some other reason?

Offline Jim

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If the RCS can also operate at all altitudes,


No such thing.

Do you say this because it's not possible to design one nozzle that's optimized for all ambient pressures? Or for some other reason?

Thrusters don't have enough power to over come aero forces.  If they do, they are grossly over sized.

Offline adrianwyard

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Aha. Thanks, makes sense.

Offline adrianwyard

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I see the Shuttle orbiter's vernier jets were a scant 25 pounds-force, and main RCS jets were 860 pounds-force. Since DC is ~1/10th the mass of the orbiter, can we guess its' RCS will be closer in size to the Shuttle's verniers?

Offline Lars_J

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I see the Shuttle orbiter's vernier jets were a scant 25 pounds-force, and main RCS jets were 860 pounds-force. Since DC is ~1/10th the mass of the orbiter, can we guess its' RCS will be closer in size to the Shuttle's verniers?

For comparison, Dragon uses 90 lbf thrusters for a much smaller spacecraft, but that is probably an upper bound for what one can expect. (Dracos are a bit oversized due to having to work as deorbit engines as well)

Offline Rocket Science

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All those thrusters are pretty much like throwing “wet Kleenex” out the window expecting a change in direction down here at 1g... ;D
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Offline deltaV

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How about towing behind an F15 or F15E for high altitude tests? Those fighters seem to be about the right size for towing Dream Chaser and their insane T/W would make reaching the needed takeoff speed within a reasonable length runway easy.

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