Author Topic: Dream Chaser aims to use Space Shuttle’s legacy to its advantage  (Read 13408 times)

Offline vulture4

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I recognize that there are different opinions on the advantages of different aerodynamic entry vehicles. To my knowledge there has never been an actual engineering trade study directly comparing winged and wingless runway landing entry vehicles.

However having supported almost a hundred Shuttle landings, some very close to the margins, many others waved off because conditions were not ideal, it is not easy for me to understand why anyone would want to have less than the optimal lift and drag, and the minimal touchdown speed and the best possible final approach performance margins. If you don't think touchdown speed is important, the next time you get on an airliner ask the pilot if he'd like to land without flaps.

Wingless lifting bodies were first investigated because in the early 60's it was doubted that any material could be found that would tolerate the aerodynamic heating of a sharp leading edge. The Shuttle had wings because the necessary materials were developed and because, after over a decade of trying, there was no lifting body that could approach the performance of a winged vehicle. The Shuttle had better aerodynamic performance than any lifting body, even though they were boat-tailed and the Shuttle had huge engine bells that caused almost half its drag. With the tail cone installed the Shuttle has twice the L/D of the best wingless lifting body, an unimaginable difference in aviation, and that becomes particularly important as landing mass is increased. If you want more drag, you can always deploy a speed brake. If you want more lift (with the separated wing and tail of the X-37) you can lower the flaps. Just my opinion. Feel free to disagree.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070017478_2007014601.pdf
Here's the X-37; note low sink rate at touchdown in the third landing.
« Last Edit: 08/21/2012 02:15 AM by vulture4 »

Offline john smith 19

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However having supported almost a hundred Shuttle landings, some very close to the margins, many others waved off because conditions were not ideal,
Shuttle landings were unpowered. Due to them needing 5 mile visibility (because STS was not certified for instrument landing) and sitting on tires that were only rated to c 188knots landing speed if conditions were not *perfect* then reentry did not take place. Proposals as simple as changing some of the autopilot constants and logic could have fixed this.

Quote
Wingless lifting bodies were first investigated because in the early 60's it was doubted that any material could be found that would tolerate the aerodynamic heating of a sharp leading edge.
ACtually Reinfoced Carbon Carbon dates from around this time and was IIRC one of the options for the X20 Dyan Soar nose. For this kind of reentry it's not *peak* temperature given by rate of heat input (q dot) it's *total* heat input (Q) that was the problem.

Quote
The Shuttle had wings because the necessary materials were developed and because, after over a decade of trying, there was no lifting body that could approach the performance of a winged vehicle. The Shuttle had better aerodynamic performance than any lifting body, even though they were boat-tailed and the Shuttle had huge engine bells that caused almost half its drag. With the tail cone installed the Shuttle has twice the L/D of the best wingless lifting body, an unimaginable difference in aviation, and that becomes particularly important as landing mass is increased. If you want more drag, you can always deploy a speed brake. If you want more lift (with the separated wing and tail of the X-37) you can lower the flaps. Just my opinion. Feel free to disagree.
The *big* driver for wings was the USAF demand for return to launch site after 1 orbit. This required *huge* cross range, relative to a capsule design. IIRC the FDL5 lifting body design would have *global* cross range (Hypersonic L/D of something like 3.5) but would have made it a joint NASA/USAF programme (and I'm not sure if the FDL5 was still classified at that time).

BTW Orbiter wings are not "sharp" by conventional aircraft standards *relative* to the the size of the vehicle. AFAIK the shock front is still detached and in front of the leading edge.

The attractions of lifting bodies are the reduced acreage of TPS (The NASA TPS database lists replacement costs of tiles as $12000/m^2 nd blankets as $3000/m^2) and improved volumetric efficiency. You need a smaller planform and you can put stuff on top of most of the *area* of that plan form.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070017478_2007014601.pdf

A *very* nice paper. Interesting to see that what looks to be one of the design rules of thumb (Hoerners) is roughly 3x too small, which suggests some promising ideas that were evaluated with it (and failed) might have worked in IRL just fine, or vice versa (but got cancelled for other reasons before anyone tried to build them).

It's good to know people are still mining this data and not taking historic rules of thumb as gospel.

I hope designers of the *next* generation pay attention to the results.
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[unit change mph to knots.Deleted YT link]
« Last Edit: 08/22/2012 07:34 AM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline Jim

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Proposals as simple as changing some of the autopilot constants and logic could have fixed this.


Not true by any means. 

Offline john smith 19

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Proposals as simple as changing some of the autopilot constants and logic could have fixed this.


Not true by any means. 
On reading the report again
 " Evaluation of Potential Changes to the Space Shuttle Orbiter's Flight Control System to Increase Directional Control During Post Landing Rollout"

I realized I'd over simplified and conflated it with an AIAA report on how Shuttle lessons learned could assist a next generation vehicle. One of the key issues (in that report) was the Shuttle's inability to cope with any substantial cross winds.

With Shuttle gone the suggested solution to this is academic but the *issue* remains. DC's ability to land in cross winds is important if they don't want to have the same constraints on launch day weather (to handle aborts) as well as landing day weather that Shuttle had.

I hope DC will do better (shuttle weights evolved upward and it looked as if the landing gear and tire design did not keep up) but I guess that uncertainty was one of the other reasons the lifting body concept has never had a full scale workout.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline zerm

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Ok zerm took your advice and looked it up.

Here's a couple of good links I found. I didn't know who these guys were before so thanks for enlightening me.  ;D

http://www.nasa.gov/centers/dryden/news/NewsReleases/2005/05-13_prt.htm

http://www.nasa.gov/centers/dryden/news/Biographies/Pilots/bd-dfrc-p018.html

If you want to get into Lifting Bodies, both of their books are a must read as is "From Runway to Orbit" by Kenneth W. Hiff and Curtis L. Peebles.

I find that the conversation gets far more palatable when we have a greater scope of distinction of vehicles and shapes other than something on the level of; this one has things sticking out of it and that one does not. ;) Besides, the study of the history of lifting bodies serves to get you more excited about the rise of the former HL-20 shape into the SNC Dream Chaser.

Offline Wayne Hale

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The shuttle maximized lift from different parts of its anatomy at different phases of flight.  Hypersonic lift was largely developed by the fuselage, "lifting body".  Supersonic lift was generated more by the wings, which enhanced crossrange capability.  Crossrange capability is a good thing to allow for the maximum landing options.

The shuttle main gear tire ground speed limit was 225 kts; margin testing showed that there was some capability above that.  The real concern was the "critical speed" which was a combination of rotational speed and the maximum downward force exerted on the tires - this generally occurred during derotation after passing through negative angle of attack but before the nose gear touched.  Several flight software and operational changes helped the situation.

Most shuttle landing wave-offs for Florida were due to thunderstorms in the area (same is true for launch holds).  All aerospace vehicles are susceptable to lightning and the severe turbulence associated with thunderstorms.  This is true for capsules, winged vehicles, lifting bodies, etc.  Having the crossrange to redesignate to another runway can help, so can having loiter capability if you want to carry jet engines and jet fuel.

Offline BrightLight

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Being that I don't know what the DC CDR requires, just for reference this is a set of definitions of a CDR

"Critical Design Review (CDR)

The CDR demonstrates that the maturity of the design is appropriate to support proceeding with full-scale fabrication, assembly, integration, and test. CDR determines that the technical effort is on track to complete the flight and ground system development and mission operations, meeting mission performance requirements within the identified cost and schedule constraints.[3]

The following are typical objectives of a CDR:

    Ensure that the "build-to" baseline contains detailed hardware and software specifications that can meet functional and performance requirements
    Ensure that the design has been satisfactorily audited by production, verification, operations, and other specialty engineering organizations
    Ensure that the production processes and controls are sufficient to proceed to the fabrication stage
    Establish that planned Quality Assurance (QA) activities will establish perceptive verification and screening processes for producing a quality product
    Verify that the final design fulfills the specifications established at PDR"

from wikipedia.

Offline yg1968

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This article on Orion's CDR in 2015 also explains what CDR is for a spacecraft such as Orion but it should also fit for DC:
http://www.nasaspaceflight.com/2012/01/eft-1-spring-2014-launch-date-contract-negotiations/

Quote
“The CDR is a critical DDT&E milestone, where the contractor discloses its complete spacecraft system design in full detail, identifying areas where technical problems and design anomalies have been resolved,” the document states.

“Successful completion of the CDR will validate that the contractor’s spacecraft design maturity is at an acceptable level that justifies the decision to initiate fabrication/manufacturing, integration and verification of the flight hardware and software.”

In any event, DC will almost get to CDR at the end of the CCiCap base period in 2014 but not quite. I hope that NASA will exercise the CCiCap optional milestones that will allow it to get to CDR prior to making any further down selection in 2014 or 2015. 
« Last Edit: 08/24/2012 05:01 PM by yg1968 »

Offline BrightLight

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This article on Orion's CDR in 2015 also explains what CDR is for a spacecraft such as Orion but it should also fit for DC:
http://www.nasaspaceflight.com/2012/01/eft-1-spring-2014-launch-date-contract-negotiations/

Quote
“The CDR is a critical DDT&E milestone, where the contractor discloses its complete spacecraft system design in full detail, identifying areas where technical problems and design anomalies have been resolved,” the document states.

“Successful completion of the CDR will validate that the contractor’s spacecraft design maturity is at an acceptable level that justifies the decision to initiate fabrication/manufacturing, integration and verification of the flight hardware and software.”

In any event, DC will almost get to CDR at the end of the CCiCap base period in 2014 but not quite. I hope that NASA will exercise the CCiCap optional milestones that will allow it to get to CDR prior to making any further down selection in 2014 or 2015. 
This response and my post (#26) are consistent - good!
The milestones for DC CCiCap do not include CDR. Then, if an optional milestone is required for DC to perform the CDR, how much will it cost and what is the incremental work that needs to be performed to get there?
Being that I'm an optimist, I assume that there will be funds available for SNC to get the work done.

Offline yg1968

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The optional milestones have been redacted because they were considered to be propietary. So nobody knows for sure. Gerst only said that DC had optional milestones that could get them to CDR if they are exercised by NASA.

Offline BrightLight

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The optional milestones have been redacted because they were considered to be propietary. So nobody knows for sure. Gerst only said that DC had optional milestones that could get them to CDR if they are exercised by NASA.
I saw the redaction too, SNC appears to have a good record of completing milestones on time, with some luck they will make there schedule and see the extra milestones added.

Offline john smith 19

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I saw the redaction too, SNC appears to have a good record of completing milestones on time, with some luck they will make there schedule and see the extra milestones added.
As always "funding permitting"

Which will need lobbying to ensure money is in the 2014 budget.

Perhaps a little note to your local members of the Legislature, along with Frank Wolf (R-VA) who came up with the 2.5 Awards scheme.

"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

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