Author Topic: Sierra Nevada’s 5-year partnership with NASA - Progress on Dream Chaser  (Read 52037 times)

Offline Danderman

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I really like the focus the article puts on the launch vehicle configuration. It's an Atlas 4xx because it flies with the Centaur exposed rather than enclosed; it has no fairing.

Atlas 4xx has a limit of about 20,000 lbs for payload. Does the DreamChaser really have such a low weight?

Offline Rocket Science

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This was how a pad abort was simulated for the HL-20:

http://www.coe.pku.edu.cn/tpic/2011721145939517.pdf

"The laws of physics are unforgiving"
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Offline dbooker

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I read another article that said the Dream Chaser was going to have thousands of tiles.  It doesn't seem like it is going to be very cost efficient totally replacing all damaged tiles, even if only scratched.  Plus the docking adapter is only one time use?  While I'm really rooting Dream Chaser I wonder if it is really a sustainable model.  Yeah, it will cost less than a shuttle to launch but less than a Dragon? 

And it doesn't seem like it will have early abort capability.  What if the there is a fault that causes an Atlas engine shutdown 10 seconds after launch.  Will those hybrid rockets on the Dream Chaser really have the thrust to safely allow the vehicle to get away?  And what happens when that thrust hits the oxygen and hydrogen in the Centaur?

Offline Lee Jay

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I read another article that said the Dream Chaser was going to have thousands of tiles.  It doesn't seem like it is going to be very cost efficient totally replacing all damaged tiles, even if only scratched.

Remember DC is many times smaller than Shuttle (as my visit yesterday to Udvar Hazy drove home in abundance).

Quote
And it doesn't seem like it will have early abort capability.

They told me it has anytime abort capability.
« Last Edit: 06/23/2012 05:29 pm by Lee Jay »

Offline Zero-G

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I'm a bit confused though about emergency egress. I get the bit shown in the photo where a gangplank from the existing mobile launch platform gets the crew into the vehicle. But what if they need to get down in a hurry? (I'm hoping the answer involves a zip-line! :))

For a launch pad abort, SNC is looking at a separation of Dream Chaser from the Atlas V 402 stack and subsequent landing on a nearby runway, thereby eliminating the need for an emergency egress system for the crew at the pad. How that Pad Abort going to happen? I'm not sure. But that's what Mark Sirangelo noted in his interview with Lee Jay.

What would the pad crew, who is assisting the astronauts, do, if they need to get away from the pad and the rocket in a hurry? (Or the astronauts, when they are not settled in yet.)
« Last Edit: 06/23/2012 07:26 pm by Zero-G »
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Offline vt_hokie

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I envy the folks who are making this stuff happen - I'd love to work on a project like this one!

Offline Dappa

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I really like the focus the article puts on the launch vehicle configuration. It's an Atlas 4xx because it flies with the Centaur exposed rather than enclosed; it has no fairing.
Wouldn't dropping the fairing make it an x02 instead of a 4xx? ;) There's no 4m fairing (x), no solids (0), and a dual engine Centaur(2).;D


Atlas 4xx has a limit of about 20,000 lbs for payload. Does the DreamChaser really have such a low weight?
The DC might not actually have such a low weight. There are several factors that could benefit the (required) performance.
- No payload faring, reducing weight on the Atlas.
- Altlas 402 (x02?), not the 401 we are used to. Better performance to LEO because of the dual engine Centaur.
- DC might do an OMS-2 or even an OMS-1 style burn, lowering the dV requirement on the Atlas.
« Last Edit: 06/24/2012 12:11 pm by Dappa »

Offline laszlo

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I read another article that said the Dream Chaser was going to have thousands of tiles.  It doesn't seem like it is going to be very cost efficient totally replacing all damaged tiles, even if only scratched.  Plus the docking adapter is only one time use?...

The tiles are mounted on a modular carrier. Replacing them is more like changing the cowling on an aircraft (minutes) than retiling your shower (days).

The entire booster is only used one time, why worry about the docking adapter? Consider it part of the booster. Seriously, if it's cheaper to make a new one than to refurbish the old, what's the problem?

Cheers,

Laszlo

Offline Jim

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The entire booster is only used one time, why worry about the docking adapter? Consider it part of the booster. Seriously, if it's cheaper to make a new one than to refurbish the old, what's the problem?

Because it is not part of the booster.  It is a integral part of the spacecraft and its pressure vessel.

Offline Rocket Science

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Quote

I'm a bit confused though about emergency egress. I get the bit shown in the photo where a gangplank from the existing mobile launch platform gets the crew into the vehicle. But what if they need to get down in a hurry? (I'm hoping the answer involves a zip-line! :))

For a launch pad abort, SNC is looking at a separation of Dream Chaser from the Atlas V 402 stack and subsequent landing on a nearby runway, thereby eliminating the need for an emergency egress system for the crew at the pad. How that Pad Abort going to happen? I'm not sure. But that's what Mark Sirangelo noted in his interview with Lee Jay.

What would the pad crew, who is assisting the astronauts, do, if they need to get away from the pad and the rocket in a hurry? (Or the astronauts, when they are not settled in yet.)
Pad safety is an important issue for both the close-out crew and flight crew. I would believe that would be part of the agreement with SNC and the launch services provider ULA. There are multiple possible scenarios possible that could happen that would require immediate evacuation (a partial crew ingress situation or just about complete etc…). The worst case of course would be would be crew a full-up pad abort and landing at the SLF or the “Skid Strip” runway. The hard lessons learned from Apollo 1 I’m sure has not been forgotten.  Perhaps Jim can illuminate changes to the pad on ULA’s side in preparation for services, being more than common to both Dream Chaser's or CST-100’s needs.
« Last Edit: 06/24/2012 01:00 pm by Rocket Science »
"The laws of physics are unforgiving"
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Offline laszlo

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The entire booster is only used one time, why worry about the docking adapter? Consider it part of the booster. Seriously, if it's cheaper to make a new one than to refurbish the old, what's the problem?

Because it is not part of the booster.  It is a integral part of the spacecraft and its pressure vessel.

So much for using humorous rhetorical questions to make a point.

It's still not a problem. It's the 21st Century and we have bolt & gasket technology. Don't confuse integral with permanent.


Offline Jim

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So much for using humorous rhetorical questions to make a point.

It's still not a problem. It's the 21st Century and we have bolt & gasket technology. Don't confuse integral with permanent.


Your point and humor failed because it is wrong. Don't confuse technology as a fix for proper engineering.
« Last Edit: 06/24/2012 01:32 pm by Jim »

Offline Lee Jay

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So much for using humorous rhetorical questions to make a point.

It's still not a problem. It's the 21st Century and we have bolt & gasket technology. Don't confuse integral with permanent.


Your point and humor failed because it is wrong. Don't confuse technology as a fix for proper engineering.


Doesn't SpaceX jettison Dragon's docking adapter before entry?

Offline mr. mark

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So much for using humorous rhetorical questions to make a point.

It's still not a problem. It's the 21st Century and we have bolt & gasket technology. Don't confuse integral with permanent.


Your point and humor failed because it is wrong. Don't confuse technology as a fix for proper engineering.


Doesn't SpaceX jettison Dragon's docking adapter before entry?
I don't think so, have to look into that. From what I'm hearing, a two month turnaround at best for Dreamchaser. So what is being advertised to the public as a quick turnaround vehicle is just not so.

Offline Lee Jay

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From what I'm hearing, a two month turnaround at best for Dreamchaser. So what is being advertised to the public as a quick turnaround vehicle is just not so.

Typical orbiter turnarounds were three times as long.

Offline Rocket Science

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They will build multiple vehicles so that will factor into the plus side how many launches take place over a year… ;)
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator

Offline mike robel

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I really like this vehicle.  But I worry a little about the Clean Room graphic at the end of the article.  It reminds me of the early shuttle processing concepts.

Still, a great article!  Thanks Chris and NSF.

Offline Danderman

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Atlas 4xx has a limit of about 20,000 lbs for payload. Does the DreamChaser really have such a low weight?
The DC might not actually have such a low weight. There are several factors that could benefit the (required) performance.
- No payload faring, reducing weight on the Atlas.
- Altlas 402 (x02?), not the 401 we are used to. Better performance to LEO because of the dual engine Centaur.
- DC might do an OMS-2 or even an OMS-1 style burn, lowering the dV requirement on the Atlas.

Its a structural loads issue, not a payload performance issue. Atlas 4xx actually can orbit more mass than it can lift with 2 RL-10s in the Centaur.

Offline laszlo

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So much for using humorous rhetorical questions to make a point.

It's still not a problem. It's the 21st Century and we have bolt & gasket technology. Don't confuse integral with permanent.


Your point and humor failed because it is wrong. Don't confuse technology as a fix for proper engineering.


Proper engineering? Is it not proper engineering when a spacecraft temporarily modifies its pressure vessel by attaching a space station or another spacecraft to it?

For that matter, how is replacing the docking adapter after the flight different from swapping out any other component?

The actual question was about the desirability of refurbishing vs. replacing. Sierra Nevada has decided that it's more cost-effective to replace. Since it's their spacecraft and design, they ought to know.

Offline Jim

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For that matter, how is replacing the docking adapter after the flight different from swapping out any other component?


Other components do not deal with the pressure vessel.

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