Pros and Cons, Dragon V2, CST-100 and Dream Chaser

[JazzFan]

21st century LEO ops should not include a return to Earth that looks like a SAR operation. We live on a planetary body that has an atmosphere so why not use it for landing. It’s free and always there and DC’s lifting body maximizes it utilization to the greatest effect...

Good point.  Both a glider and an F22 are capable of manned flight and landing even with radically different vehicles.  Is the goal of the crew vehicle to simply return or to return with accuracy?  If with accuracy, then DC's design is definitely a pro.

[Robotbeat]

Dragon can also land with accuracy and has better survivability due to being a capsule.

Also, the best way to ensure that Russia will never stop shipments of RD-180 is to ensure that there is a well-exercised alternative. That gives them much less leverage if Dragon is used as one of the options. After all, this is one of the main reasons to do commercial crew in the first place! It ensures the Russians don't have any reason to play tough with Soyuz.

[Zed_Noir]

21st century LEO ops should not include a return to Earth that looks like a SAR operation. We live on a planetary body that has an atmosphere so why not use it for landing. It’s free and always there and DC’s lifting body maximizes it utilization to the greatest effect...

You will have a SAR operation ready to rolled anytime there is a manned spacecraft reentry.

The DC does a one pass dead stick landing glide. Which means it will not be at a landing facility with other schedule flights. It will land most likely at an isolated specialized facility.

[vt_hokie]

The DC does a one pass dead stick landing glide. Which means it will not be at a landing facility with other schedule flights. It will land most likely at an isolated specialized facility.

I've done a dead stick landing into a facility with other scheduled flights!  Or, more accurately, my instructor has... 



But in all seriousness, I think the low-G reentry profile and runway touchdown capability of Dream Chaser would be particularly attractive in the assured crew return vehicle role. 

[arachnitect]

Parachute landings can never be commonplace to a healthy commercial spaceflight industry.

Of all the inconveniences of flying in space, I'd say this is about 1000th down the list.

I think Boeing made a smart move making a modest development effort to get land landings, without really having to invent anything new.

Speaking of bad weather at the landing site for the two capsules, wouldn't the Dragon's powered landing system provide them with better control in windy conditions?  And if they don't pop their chute they have less chance of being dragged around in high winds after landing.  No doubt there is a limit to how windy they could land in, but I would think powered landings could be more safe from that aspect.

All the vehicles will have operational limitations, Dragon/DC are not immune to weather. Will Dragon land in conditions that are too windy for the reserve chutes to work safely?

[Rocket Science]

21st century LEO ops should not include a return to Earth that looks like a SAR operation. We live on a planetary body that has an atmosphere so why not use it for landing. It’s free and always there and DC’s lifting body maximizes it utilization to the greatest effect...

You will have a SAR operation ready to rolled anytime there is a manned spacecraft reentry.

The DC does a one pass dead stick landing glide. Which means it will not be at a landing facility with other schedule flights. It will land most likely at an isolated specialized facility.

SAR is ready to roll every time I take my plane up if the ELT triggers it...  That isolated specialized facility will be primary KSC SLF with a short roll-over for processing...

[oiorionsbelt]

what I'm asking is how this would compare to flying a traditional throwaway escape rocket that would jettison and thus eliminate the need to carry that substantial mass all the way to orbit and back. 
 - Ed Kyle

One result is that aborts are not available all the way to orbit.

[edkyle99]

what I'm asking is how this would compare to flying a traditional throwaway escape rocket that would jettison and thus eliminate the need to carry that substantial mass all the way to orbit and back. 
 - Ed Kyle

One result is that aborts are not available all the way to orbit.

After the initial launch phase, abort options do not require a high thrust launch escape system.  Apollo could abort all the way to orbit during its 11 minute ascent, but its 3.6 tonne LES was jettisoned after only three minutes.

 - Ed Kyle 

[oiorionsbelt]

While watching the traditional tractor abort system tests of the Orion Spacecraft  I'm struck by the clumsiness and inelegance of that system. So many events, so many parts. It appears, to my untrained eye, to be extremely limited, expensive, heavy, inefficient and fraught with failure modes. DV2's approach seems simple, elegant, relatively cheap and as others have said nothing is wasted.

[Roy_H]

Bigelow contributed $100M to the development of CTS-100.

Source?

I spent some time trying to find it without success. Probably in one of the articles listed here: http://bigelowaerospace.com/in-the-news.php but many are broken or point to to-days headlines rather than 8 years ago. The best I could find was this: http://boeing.mediaroom.com/index.php?s=20295&item=1054
"As part of the Boeing CCDev team, Las Vegas-based Bigelow Aerospace will provide requirements for crew transportation to support its planned Orbital Space Complex, as well as additional investment and expertise in testing and validating the technologies necessary to construct and deploy the complex."

[QuantumG]

There was a lot of confusion at the time about what Bigelow's status in the Boeing CST program was.. with the word "partner" being thrown around a lot. Moon and Back eventually got an interview with Bob Bigelow and asked what the relationship was.. Bigelow was a subcontractor, not a partner. The money ran down hill from NASA to Boeing to Bigelow. There was no reverse investment.

It's somewhere in this four part video series:

[Jim]

While watching the traditional tractor abort system tests of the Orion Spacecraft  I'm struck by the clumsiness and inelegance of that system. So many events, so many parts. It appears, to my untrained eye, to be extremely limited, expensive, heavy, inefficient and fraught with failure modes. DV2's approach seems simple, elegant, relatively cheap and as others have said nothing is wasted.

Nonsense.  The tractor is simpler and only needs one motor to really work (the control motor doesn't have to in the dire emergency).   It doesn't have a dual use much like an ejection seat and so it is only designed to do the one task.  It has much less parts.

[clongton]

The only problem I see with a tractor motor abort mechanism is that it is single use and then is abandoned, hopefully without having been used. But the larger the spacecraft, the more massive that tractor becomes, robbing the spacecraft of mass sensitive capability. At some point the abort mechanism needs to become dual use so that the mass dedicated to it isn't wasted. Tractors work well on small spacecraft, like Mercury and Apollo. Any spacecraft larger than that using tractor abort is wasting the abort mass. All three commercial crew contenders wisely made that shift.

[darkenfast]

The DC does a one pass dead stick landing glide. Which means it will not be at a landing facility with other schedule flights. It will land most likely at an isolated specialized facility.

I've done a dead stick landing into a facility with other scheduled flights!  Or, more accurately, my instructor has... 



But in all seriousness, I think the low-G reentry profile and runway touchdown capability of Dream Chaser would be particularly attractive in the assured crew return vehicle role. 

Love the video!  I believe that the low-g reentry will only be a plus for long-duration flyers if the seats are moved to a supine position, as was the case with the Orbiters mid-deck seats.  I've yet to see any information on whether or not this is planned for Dream Chaser.  Does anyone know?  Or has someone concluded that sitting upright at about 1.5g is no worse than 3-4g on your back?  Did the Shuttle ever bring any long-stay crew back in upright seats, and if so, what were the results?

As for the argument regarding wings/lifting bodies vs. capsules, I don't think that this forum will EVER reach a consensus.  DC uses the air to handle everything from re-entry down to touchdown, but has to carry the structure, fins and landing gear to do so and has to deal with major loads in two directions.  Dragon uses the air down to the last 400 or so MPH, and then will use rockets and/or chutes that are already there for other reasons to accomplish what hopefully will be pin-point landings.  CST ditto down to about 400 mph, then will use just chutes and airbags but will need something like Edwards to land at.  The capsules are (possibly), stronger for weight, because of their shape and how they carry loads, but need heat shields.  How does the weight penalty for capsule heat shields vs. the system on DC stack up?   All three should work, but I personally think that capsules are more efficient with the present technology.  Build something like Skylon and THEN we can play with wings again. 

[heinkel174]

While watching the traditional tractor abort system tests of the Orion Spacecraft  I'm struck by the clumsiness and inelegance of that system. So many events, so many parts. It appears, to my untrained eye, to be extremely limited, expensive, heavy, inefficient and fraught with failure modes. DV2's approach seems simple, elegant, relatively cheap and as others have said nothing is wasted.

From the view point of flight control, a tractor system is inherently simpler and more stable than a pusher system. When the abort motor is working the CoG of the stack is far below the center of thrust so the capsule effectively act as a stabilizer. It’s bad for a vehicle that requires agility, but all you want of a LAS is to pull the capsule up and high really fast with blunt force. 

And exactly what is clumsiness in the Orion LAS? It only has three motors. The abort motor is a big dumb booster, the jettison motor is also a no-brainer. Only the attitude control motor looks a bit clumsy, but it is really just one solid motor with many controllable exhausts (so you don’t have to gimbal the nozzle). I think it looks inelegant primarily because of the dirty solid engine exhaust.

[Coastal Ron]

And exactly what is clumsiness in the Orion LAS? It only has three motors.

According to a 2011 NASA fact sheet, the entire Orion stack is 69,181 lbs, of which the LAS is 16,125 lbs.  That's about 25% of the whole system.

Anyone have a guess what the equivalents would be for Dragon V2, CST-100 and Dream Chaser?  My guess would be less.

[ChrisWilson68]

21st century LEO ops should not include a return to Earth that looks like a SAR operation. We live on a planetary body that has an atmosphere so why not use it for landing. It’s free and always there and DC’s lifting body maximizes it utilization to the greatest effect...

The atmosphere is free, but the structure to make use of it is not.  That structure imposes various costs on a landing vehicle.

[Robotbeat]

While watching the traditional tractor abort system tests of the Orion Spacecraft  I'm struck by the clumsiness and inelegance of that system. So many events, so many parts. It appears, to my untrained eye, to be extremely limited, expensive, heavy, inefficient and fraught with failure modes. DV2's approach seems simple, elegant, relatively cheap and as others have said nothing is wasted.

Nonsense.  The tractor is simpler and only needs one motor to really work (the control motor doesn't have to in the dire emergency).   It doesn't have a dual use much like an ejection seat and so it is only designed to do the one task.  It has much less parts.

Nevertheless, the Orion abort motor has three solid rockets, one with a very complicated and unique thrust vectoring method. The whole LAS is disproportionately heavy given the mass of The Orion capsule, worse than Apollo. And worst of all: if the jettison motor doesn't work every single time, the crew dies. The LAS actually introduces a significant failure point. All the commercial crew systems are superior in this respect.

[ChrisWilson68]

From the view point of flight control, a tractor system is inherently simpler and more stable than a pusher system. When the abort motor is working the CoG of the stack is far below the center of thrust so the capsule effectively act as a stabilizer.

That's what Robert Goddard thought, which is why he built his early rocket as a tractor.  Eventually he realized it isn't true at all that a tractor is more stable.  It's now called the Pendulum Rocket Fallacy.

http://en.wikipedia.org/wiki/Pendulum_rocket_fallacy

[pagheca]

While watching the traditional tractor abort system tests of the Orion Spacecraft  I'm struck by the clumsiness and inelegance of that system. So many events, so many parts. It appears, to my untrained eye, to be extremely limited, expensive, heavy, inefficient and fraught with failure modes. DV2's approach seems simple, elegant, relatively cheap and as others have said nothing is wasted.

I understood that - as usual with complex engineering systems - there are pros and cons while comparing tractors and pushers. For example:

Each system has advantages and disadvantages compared to the other. For example, an Apollo-style tractor rocket mounted atop the capsule can allow more mass to be taken into orbit, Totton said. A tower also ignites quickly and builds up its thrust very fast to escape danger. On the other hand, if there is not an abort, the tower is thrown away.

A pusher system, with all the weight of the spacecraft above it instead of below, can put more pressure on the computers controlling the abort during the critical first second or so when the spacecraft is getting away from the rocket.

[...]

On the plus side, the engines and propellant not used in an abort can still be used by the spacecraft once it reaches orbit. SpaceX, for example, has expressed interest in using the engines at landing to make pinpoint returns to a pad on Earth after a mission.

"A pusher becomes very synergetic to the overall mission," Gerace said.

Previously, liquid-fueled pusher engines were not practical for an abort system because they didn't build up thrust quickly enough. Jett said engine technology advances have closed that gap, though.
[...]

I think there is no nonsense in either opinion. The devil is, again, as usual, in the details. With the same over-simplified aesthetic-driven logic one could say that a solid rocket is better because simpler than a liquid rocket. We all know that this is not always (aka necessarily) true. The Orion abort system seems to me to be driven by a set of specs that are not easy to be balanced to maximize crew survival probability. I cannot see a clumsy system but an hard to solve multi parametric equation.

Interesting debate, anyway.