SERV/DC-X reboot

[sevenperforce]

If you aren't familiar with the Chrysler SERV concept, check it out. Quite possibly the most innovative of the proposed Shuttle concepts, though it was never seriously considered. The military need for crossrange maneuvering during abort-once-around polar orbit launches, coupled with a lack of reliably restartable rocket engines, led to them adding dozens of jet engines to the design...which really doomed it.

But with the air augmentation of a ducted rocket design, inner side-mounted deeply throttleable linear engines, and an overall ballistic re-entry profile, this could be promising. The crew-carrying variant would be mated at the top to a Dragon V2 capsule, while the cargo variant would hold an internal payload ducting would allow for weight-free afterburn injection to increase launch thrust for larger payloads with an extended upper fairing:

The ducts at the top would allow maximum airflow and thrust augmentation without adding significant drag:

The lower base would have a passive heat shield, dissipating heat both around the body and up through the heat-resistant ducting. The linear engines are positioned in such a way as to make maximal use of the atmosphere, from aerospike effect and thrust augmentation all the way up into vacuum operation, without needing to use any moveable flaps or panels:

Downstream injectors (not shown) allow for added thrust at takeoff, using a denser fuel (yes, I favor hydrazine) to combust with the existing exhaust stream and the airflow. This would be used when the extended fairing holds a heavier payload and requires additional thrust. Although this requires a greater weight of fuel, thrust augmentation would be significant enough to increase the T/W overall and keep the total dV constant.

Due to the possibility of afterburn-style thrust augmentation, this vehicle can have its thrust increased dramatically at the cost of reduced delta-v, making it a fantastic super-heavy lift first stage.

After reaching orbit and ejecting payload, re-entry would take place using the base heat shield, landing on a hover at the launch pad with the throttleable main engines. In no case would re-entry be manned, as the capsule would re-enter separately. Since orbit would be achieved on virtually all missions (with the exception of super-heavy lift scenarios as noted above), this wouldn't have the SpaceX downrange problem or need to land on a barge; it could just abort once around and come back to the launch pad every time.

Edited February 29, 2016 by sevenperforce

[kunok]

I fail to see the relation with the DC-X, only being a VTVL SSTO, but isn't similar.

[magnemoe]

Do not know much about air augmented rockets but the ones I have seen has far smaller air intakes.
Idea makes some sense if you don't launch from Florida, with air augmented you want an pretty flat first stage trajectory, and is has to be two stages, air augmented is not real air breather more like an higher isp rocket. and have fun trying to deorbit with it. Launch from texas and land in the Caribbean perhaps. You can do an braking or redirect burn but is likely to go hypersonic at separation .

[fredinno]

4 hours ago, sevenperforce said:

If you aren't familiar with the Chrysler SERV concept, check it out. Quite possibly the most innovative of the proposed Shuttle concepts, though it was never seriously considered. The military need for crossrange maneuvering during abort-once-around polar orbit launches, coupled with a lack of reliably restartable rocket engines, led to them adding dozens of jet engines to the design...which really doomed it.

But with the air augmentation of a ducted rocket design, inner side-mounted deeply throttleable linear engines, and an overall ballistic re-entry profile, this could be promising. The crew-carrying variant would be mated at the top to a Dragon V2 capsule, while the cargo variant would hold an internal payload ducting would allow for weight-free afterburn injection to increase launch thrust for larger payloads with an extended upper fairing:

The ducts at the top would allow maximum airflow and thrust augmentation without adding significant drag:

The lower base would have a passive heat shield, dissipating heat both around the body and up through the heat-resistant ducting. The linear engines are positioned in such a way as to make maximal use of the atmosphere, from aerospike effect and thrust augmentation all the way up into vacuum operation, without needing to use any moveable flaps or panels:

Downstream injectors (not shown) allow for added thrust at takeoff, using a denser fuel (yes, I favor hydrazine) to combust with the existing exhaust stream and the airflow. This would be used when the extended fairing holds a heavier payload and requires additional thrust. Although this requires a greater weight of fuel, thrust augmentation would be significant enough to increase the T/W overall and keep the total dV constant.

Due to the possibility of afterburn-style thrust augmentation, this vehicle can have its thrust increased dramatically at the cost of reduced delta-v, making it a fantastic super-heavy lift first stage.

After reaching orbit and ejecting payload, re-entry would take place using the base heat shield, landing on a hover at the launch pad with the throttleable main engines. In no case would re-entry be manned, as the capsule would re-enter separately. Since orbit would be achieved on virtually all missions (with the exception of super-heavy lift scenarios as noted above), this wouldn't have the SpaceX downrange problem or need to land on a barge; it could just abort once around and come back to the launch pad every time.

The payload capacoty is likely larger than a Dragon V2. Also, the payload faring is shaped wrong, (needs to be pointed) and hydrazine will raise the reuse costs a lot due to toxicity. I would go with NO2 if you need a mono-propellant.

[DerekL1963]

8 hours ago, sevenperforce said:

The military need for crossrange maneuvering during abort-once-around polar orbit launches, coupled with a lack of reliably restartable rocket engines, led to them adding dozens of jet engines to the design...which really doomed it.

The military increased the requirement for crossrange, but they didn't establish the requirement. - That originated within NASA itself, as when they finally actually looked at operations, they discovered that cross range was very useful.  Cross range increases abort opportunities and widens the windows, and the same for landing.  

8 hours ago, sevenperforce said:

But with the air augmentation of a ducted rocket design, inner side-mounted deeply throttleable linear engines, and an overall ballistic re-entry profile, this could be promising.

Not really.  With a complex and heavy system to control the shocks in the inlets, the duct isn't going to be all that effective - more a source of drag than propulsion augmentation.   (Fixed ducts like to perform in a fairly narrow range of altitudes and speeds - which is precisely what rockets don't fly anything like.)

And good luck trying to keep those sharp edges at the base of your ducts from burning away during re-entry...  and in keeping re-entry plasma away from the walls of the ducts.

8 hours ago, sevenperforce said:

In no case would re-entry be manned, as the capsule would re-enter separately.

Why would you do something so supremely silly as to increase the risks to the crew by adding a separation event, and reduce the performance of the vehicle by adding in the weight of all the stuff needed for the crew capsule to re-enter and land?

[tater]

As I recall, the original SERV design carried a lifting body or winged crew shuttle. Lemme see if I can find a picture.

[tater]

 

[fredinno]

32 minutes ago, DerekL1963 said:

The military increased the requirement for crossrange, but they didn't establish the requirement. - That originated within NASA itself, as when they finally actually looked at operations, they discovered that cross range was very useful.  Cross range increases abort opportunities and widens the windows, and the same for landing.  

Not really.  With a complex and heavy system to control the shocks in the inlets, the duct isn't going to be all that effective - more a source of drag than propulsion augmentation.   (Fixed ducts like to perform in a fairly narrow range of altitudes and speeds - which is precisely what rockets don't fly anything like.)

And good luck trying to keep those sharp edges at the base of your ducts from burning away during re-entry...  and in keeping re-entry plasma away from the walls of the ducts.

Why would you do something so supremely silly as to increase the risks to the crew by adding a separation event, and reduce the performance of the vehicle by adding in the weight of all the stuff needed for the crew capsule to re-enter and land?

In case of abort?

[DerekL1963]

22 minutes ago, fredinno said:

54 minutes ago, DerekL1963 said:

Why would you do something so supremely silly as to increase the risks to the crew by adding a separation event, and reduce the performance of the vehicle by adding in the weight of all the stuff needed for the crew capsule to re-enter and land?

In case of abort?

And I quote from the original post, just as I did in my post.

9 hours ago, sevenperforce said:

In no case would re-entry be manned, as the capsule would re-enter separately.

It's not an abort mode - it's a normal mode.

[sevenperforce]

6 hours ago, DerekL1963 said:

7 hours ago, fredinno said:

7 hours ago, DerekL1963 said:

Why would you do something so supremely silly as to increase the risks to the crew by adding a separation event, and reduce the performance of the vehicle by adding in the weight of all the stuff needed for the crew capsule to re-enter and land?

In case of abort?

And I quote from the original post, just as I did in my post.

16 hours ago, sevenperforce said:

In no case would re-entry be manned, as the capsule would re-enter separately.

It's not an abort mode - it's a normal mode.

Wait, I'm completely confused. What is wrong with a separation event? Particularly an on-orbit separation event? Every single spacecraft (not just manned ones) to enter orbit has had at least one separation event. This one would be far safer because it occurs in orbit.

And having a separate crew capsule which lands independently allows for catastrophic launch abort while also being safer than the alternative. It allows the rocket to be landed in the way that's best for the rocket and the capsule to be landed in the way that's best for the capsule. The capsule can have backup parachutes which would not be feasible for the rocket.

7 hours ago, DerekL1963 said:

The military increased the requirement for crossrange, but they didn't establish the requirement. - That originated within NASA itself, as when they finally actually looked at operations, they discovered that cross range was very useful.  Cross range increases abort opportunities and widens the windows, and the same for landing.

 Indeed, and this would have fine crossrange performance. It just wasn't something possible when SERV was proposed.

8 hours ago, DerekL1963 said:

With a complex and heavy system to control the shocks in the inlets, the duct isn't going to be all that effective - more a source of drag than propulsion augmentation.   (Fixed ducts like to perform in a fairly narrow range of altitudes and speeds - which is precisely what rockets don't fly anything like.)

And good luck trying to keep those sharp edges at the base of your ducts from burning away during re-entry...  and in keeping re-entry plasma away from the walls of the ducts.

The goal of the central bypass design is to allow the airflow through the duct to self-correct; the rocket would use a launch profile designed to optimize this. Not sure if this is possible; if not, I'll probably design a variable-attack-angle craft.

And yeah, I'll need to smooth the exhaust surfaces for re-entry. No problem getting re-entry plasma in the ducts, though; they're going to be handling rocket exhaust as it is.

8 hours ago, tater said:

As I recall, the original SERV design carried a lifting body or winged crew shuttle. Lemme see if I can find a picture.

The worst part of the idea.

12 hours ago, fredinno said:

The payload capacoty is likely larger than a Dragon V2. Also, the payload faring is shaped wrong, (needs to be pointed) and hydrazine will raise the reuse costs a lot due to toxicity. I would go with NO2 if you need a mono-propellant.

Yeah, the payload fairing needs to be fixed.

The ship would be scaled such that the nominal payload to LEO would be something around twice the mass of the Dragon V2; this will allow it to carry both a crew capsule and a small cargo load simultaneously. With crew capsule alone, it could probably take the capsule to the Earth-Moon Lagrange points.

You don't like hydrazine, do you? Haha. I wanted a monopropellant that could burn with the exhaust plume in the ducts and thus serve as an afterburner.

[DerekL1963]

2 hours ago, sevenperforce said:

Wait, I'm completely confused. What is wrong with a separation event? Particularly an on-orbit separation event? Every single spacecraft (not just manned ones) to enter orbit has had at least one separation event. This one would be far safer because it occurs in orbit.

o.0  You honestly don't grasp the difference between separating in order to get rid of a part that can't re-enter, and separating for vague hand waving reasons?   And no, it wouldn't be far safer - it would be far less safe because the on orbit lifetime of the capsule will be measured in hours, if something goes wrong and re-entry has to be delayed, the capsule crew is in considerable danger.

 

2 hours ago, sevenperforce said:

And having a separate crew capsule which lands independently allows for catastrophic launch abort while also being safer than the alternative. It allows the rocket to be landed in the way that's best for the rocket and the capsule to be landed in the way that's best for the capsule. The capsule can have backup parachutes which would not be feasible for the rocket.

We're not discussing aborts, we're discussing normal operations.   And what's different between the best way for the booster and the best way for the capsule?

2 hours ago, sevenperforce said:

No problem getting re-entry plasma in the ducts, though; they're going to be handling rocket exhaust as it is.

I've searched the world over, and there isn't an emoticon that expresses how boggled I am.   You do know that re-entry plasma is an order of magnitude hotter than rocket exhaust?   That no known material can withstand that direct assault? 

[SSgt Baloo]

I have a penchant for weird/odd designs. I like this one. There were some remarkable proposals being put forward WRT the space shuttle program during the late '60s and early '70s. I'd like to see some of them modeled in KSP despite their "impracticality". Weird is fun.

 

Edited March 1, 2016 by SSgt Baloo

[sevenperforce]

40 minutes ago, DerekL1963 said:

o.0  You honestly don't grasp the difference between separating in order to get rid of a part that can't re-enter, and separating for vague hand waving reasons?   And no, it wouldn't be far safer - it would be far less safe because the on orbit lifetime of the capsule will be measured in hours, if something goes wrong and re-entry has to be delayed, the capsule crew is in considerable danger.

We must be talking past each other, or something.

Would you have the crew cabin be built into the nose of the rocket, so that the rocket goes and docks with the ISS like the Shuttle did? The point is to have a RLV which can launch different payloads based on its configuration. I don't see what would be gained by building the crew cabin into the rocket body.

Why is the on-orbit lifetime of the capsule measured in hours? The Dragon V2 is supposed to have a pretty lengthy orbital manned persistence. How is it less safe to be in orbit in a Dragon V2 than in a gigantic capsule-shaped rocket?

Separation accomplishes quite a few things. For one, it returns the launch vehicle immediately, so it can be refurbished and reused while the capsule remains in orbit (or docked with the ISS) for as long as required. It also allows the whole system to be modular, so that the same launch vehicle that put a satellite into orbit last month can launch a manned capsule to the ISS this month.

47 minutes ago, DerekL1963 said:

What's different between the best way for the booster and the best way for the capsule?

Well, at the very minimum, it's easier to get a 7-tonne capsule back to Earth than it is to get a 50-tonne nearly-empty rocket back to Earth. It's something we're good at. A capsule like the Dragon V2 carries its own engines for either propulsive landing or launch abort, and (as I said) can carry backup parachutes. Keeping the entire monster in orbit and then deorbiting it with the crew cabin still in it is much less safe because it can't carry backup parachutes, and because its re-entry profile will be different. A crew capsule is optimized for one thing: returning a crew safely. The launch vehicle, on the other hand, has to be optimized first for launch and only secondarily for re-entry.

50 minutes ago, DerekL1963 said:

You do know that re-entry plasma is an order of magnitude hotter than rocket exhaust?   That no known material can withstand that direct assault? 

Yes. But the ducts go all the way through. You're using PICA-X type heat shielding on the base and it extends up into the ducts. Plus, the plasma escapes through the ducts.

 

[DerekL1963]

18 minutes ago, sevenperforce said:

1 hour ago, DerekL1963 said:

o.0  You honestly don't grasp the difference between separating in order to get rid of a part that can't re-enter, and separating for vague hand waving reasons?   And no, it wouldn't be far safer - it would be far less safe because the on orbit lifetime of the capsule will be measured in hours, if something goes wrong and re-entry has to be delayed, the capsule crew is in considerable danger.

We must be talking past each other, or something.

Would you have the crew cabin be built into the nose of the rocket, so that the rocket goes and docks with the ISS like the Shuttle did? The point is to have a RLV which can launch different payloads based on its configuration. I don't see what would be gained by building the crew cabin into the rocket body.

No, we're not talking past each other.   Did I say anything about building the crew cabin into the nose of the rocket?  No, I did not.   Did I say anything about different configurations or not?  No, I did not.   Did I say anything about building the crew cabin into the body?  No, I did not.

I asked a simple question, and when asked by you I provided amplifying information as to why I was asking.  Then instead of answering the question about apples, you went off on a discussion about oranges, pomegranates, and bicycles.
 

21 minutes ago, sevenperforce said:

Why is the on-orbit lifetime of the capsule measured in hours? The Dragon V2 is supposed to have a pretty lengthy orbital manned persistence. How is it less safe to be in orbit in a Dragon V2 than in a gigantic capsule-shaped rocket?

You do know the Dragon V2 has a service module?  There is no service module mentioned or in your illustrations, only the capsule.  And as to your last question, once again my mind boggles - we're discussing the capsule in independent flight, always have been in this sub discussion.  (And docking to ISS has never previously been mentioned.)  The safety issue occurs because you have a separation event, which can happen early or happen late, or nearly not happen at all.  (And all these things have happened to Soyuz.)  So separation events are something to be minimized if possible.

The confusion has arisen because you made the didactic statement about "capsule separation will be the normal mode" and the completely failed to provide the reason for this when asked - it took two tries to pry that information out of you.  Had you stated that vehicles mission was to deliver a capsule on orbit in the first place, this confusion would never have arisen.
 

26 minutes ago, sevenperforce said:

1 hour ago, DerekL1963 said:

What's different between the best way for the booster and the best way for the capsule?

Well, at the very minimum, it's easier to get a 7-tonne capsule back to Earth than it is to get a 50-tonne nearly-empty rocket back to Earth. It's something we're good at.

o.0  Wait, we're going to be flying a 50 ton booster routinely, and we won't get good at it?  What's the point of flying it then?

Seriously, an actual rocket is more than a collection of Really Cool parts and concepts thrown together like Lego because they're Really Cool.   You need to think through the entire operation, step by step, looking at what the mission requires and whether or not the vehicle will supply that requirement.   You also need to remember we're not inside your head - you need to explain your operational concept and not be surprised when you fail to give information and we ask for it.

[tater]

The original concept included either a SM/CM combination, or that 'MURP" (Manned Upper Reusable Payload) lifting body. There were some similar looking capsule designs floated in the 70s as VTVL HLVs (some SSTOs, others staged), but those were for large payloads, not crew transfer.

 

[sevenperforce]

11 minutes ago, DerekL1963 said:

No, we're not talking past each other.   Did I say anything about building the crew cabin into the nose of the rocket?  No, I did not.   Did I say anything about different configurations or not?  No, I did not.   Did I say anything about building the crew cabin into the body?  No, I did not.

I asked a simple question, and when asked by you I provided amplifying information as to why I was asking.

Whoa, sheesh.

You said that having a separation event was a thing to be avoided. The only alternative I could think of would be to not have a separation event, i.e., make the cabin and rocket a single body. Am I missing something?

14 minutes ago, DerekL1963 said:

You do know the Dragon V2 has a service module?  There is no service module mentioned or in your illustrations, only the capsule.  And as to your last question, once again my mind boggles - we're discussing the capsule in independent flight, always have been in this sub discussion.  (And docking to ISS has never previously been mentioned.)  The safety issue occurs because you have a separation event, which can happen early or happen late, or nearly not happen at all.  (And all these things have happened to Soyuz.)  So separation events are something to be minimized if possible.

Docking with some destination would presumably be the target. I mean, you can go up in a capsule and come down again after a couple of orbits, I suppose, but the present primary need for a manned launch vehicle is to ferry crew to the ISS.

17 minutes ago, DerekL1963 said:

o.0  Wait, we're going to be flying a 50 ton booster routinely, and we won't get good at it?  What's the point of flying it then?

Well, we'll get good at it, but we're already good at returning capsules.

The proposed model is a rocket capable of delivering payloads to orbit via SSTO. You're throwing out big warnings about one of those payloads being a manned capsule (and yes, it would obviously require a service module) and suggesting that separation is a problem. This would presumably mean you have some alternative configuration in mind...so, what would that be?

[DerekL1963]

2 hours ago, sevenperforce said:

You said that having a separation event was a thing to be avoided. The only alternative I could think of would be to not have a separation event, i.e., make the cabin and rocket a single body. Am I missing something?

Yes, you're missing what I plainly said in my previous message:

2 hours ago, DerekL1963 said:

The confusion has arisen because you made the didactic statement about "capsule separation will be the normal mode" and the completely failed to provide the reason for this when asked - it took two tries to pry that information out of you.  Had you stated that vehicles mission was to deliver a capsule on orbit in the first place, this confusion would never have arisen.

As I said above, you didn't describe the mission - that the capsule is the payload.   Your statement that "After reaching orbit and ejecting payload, re-entry would take place using the base heat shield, landing on a hover at the launch pad with the throttleable main engines. In no case would re-entry be manned, as the capsule would re-enter separately" which leads to the impression that the payload is separate from the capsule.

When the capsule is the payload rather than the command element, the separation event is inevitable.  It'll have to be accepted as one of the routine risks.

[sevenperforce]

10 minutes ago, DerekL1963 said:

As I said above, you didn't describe the mission - that the capsule is the payload.   Your statement that "After reaching orbit and ejecting payload, re-entry would take place using the base heat shield, landing on a hover at the launch pad with the throttleable main engines. In no case would re-entry be manned, as the capsule would re-enter separately" which leads to the impression that the payload is separate from the capsule.

When the capsule is the payload rather than the command element, the separation event is inevitable.  It'll have to be accepted as one of the routine risks.

I thought the capsule-as-payload configuration was pretty obviously spelled out with, "The crew-carrying variant would be mated at the top to a Dragon V2 capsule, while the cargo variant would hold an internal payload." Maybe I should have said "configuration" instead of "variant"?

Also, if you're familiar with tthe Chrysler SERV, you'd recognize the same arrangement: internal payload bay for cargo; mated at the top to a separate crew vehicle for crew transfer. 

[fredinno]

11 hours ago, sevenperforce said:

Wait, I'm completely confused. What is wrong with a separation event? Particularly an on-orbit separation event? Every single spacecraft (not just manned ones) to enter orbit has had at least one separation event. This one would be far safer because it occurs in orbit.

And having a separate crew capsule which lands independently allows for catastrophic launch abort while also being safer than the alternative. It allows the rocket to be landed in the way that's best for the rocket and the capsule to be landed in the way that's best for the capsule. The capsule can have backup parachutes which would not be feasible for the rocket.

 Indeed, and this would have fine crossrange performance. It just wasn't something possible when SERV was proposed.

The goal of the central bypass design is to allow the airflow through the duct to self-correct; the rocket would use a launch profile designed to optimize this. Not sure if this is possible; if not, I'll probably design a variable-attack-angle craft.

And yeah, I'll need to smooth the exhaust surfaces for re-entry. No problem getting re-entry plasma in the ducts, though; they're going to be handling rocket exhaust as it is.

The worst part of the idea.

Yeah, the payload fairing needs to be fixed.

The ship would be scaled such that the nominal payload to LEO would be something around twice the mass of the Dragon V2; this will allow it to carry both a crew capsule and a small cargo load simultaneously. With crew capsule alone, it could probably take the capsule to the Earth-Moon Lagrange points.

You don't like hydrazine, do you? Haha. I wanted a monopropellant that could burn with the exhaust plume in the ducts and thus serve as an afterburner.

You are overestimating the power of this rocket. You would need a lot more than one SRV for EM-L2, SLS carries a bit less than a third of its mass to LEO to EM-L2.

[magnemoe]

11 hours ago, DerekL1963 said:

You do know the Dragon V2 has a service module?  There is no service module mentioned or in your illustrations, only the capsule.  And as to your last question, once again my mind boggles - we're discussing the capsule in independent flight, always have been in this sub discussion.  (And docking to ISS has never previously been mentioned.)  The safety issue occurs because you have a separation event, which can happen early or happen late, or nearly not happen at all.  (And all these things have happened to Soyuz.)  So separation events are something to be minimized if possible.

The confusion has arisen because you made the didactic statement about "capsule separation will be the normal mode" and the completely failed to provide the reason for this when asked - it took two tries to pry that information out of you.  Had you stated that vehicles mission was to deliver a capsule on orbit in the first place, this confusion would never have arisen.

Dragons trunk is not an real service module, its hold the solar panels, radiators nothing else needed for the flight, they could probably done without it and integrated this into the pod or at least the interstage had it not been for it being needed for aerodynamic stability and to carry unpressurized cargo / secondary payload. 

[DerekL1963]

11 hours ago, magnemoe said:

Dragons trunk is not an real service module, its hold the solar panels, radiators nothing else needed for the flight, they could probably done without it and integrated this into the pod or at least the interstage had it not been for it being needed for aerodynamic stability and to carry unpressurized cargo / secondary payload. 

Whether it's a "real" service module or not is irrelevant.   What they "could" have done is irrelevant.   It does exist, and it does carry equipment which is required to extend the capsule's life beyond a few hours.

[Exoscientist]

 I think that NASA had a good idea to go first for a reusable suborbital demonstrator first before proceeding to a full SSTO in the X-33 and DC-X programs. The problem was, and it was a big one, that they did not realize the reusable suborbital vehicle itself could have been profitable.

 They were regarded as just demonstrators to do experiments on. In point of fact both the X-33 and the suborbital upgrade of the DC-X, known as the DC-Y, could have cut costs and have been profitable as reusable first stages. This could have been done 15 years ago as SpaceX is doing now.

 The key fact is if these are only needed to be first stages they don't need all the extreme weight saving steps that doomed these programs when they were only thought to be demonstrators for a SSTO.

 See the argument here:

DARPA's Spaceplane: an X-33 version.

http://exoscientist.blogspot.com/2013/10/darpas-spaceplane-x-33-version.html

 

  Bob Clark

 

 

 

[fredinno]

4 hours ago, Exoscientist said:

 I think that NASA had a good idea to go first for a reusable suborbital demonstrator first before proceeding to a full SSTO in the X-33 and DC-X programs. The problem was, and it was a big one, that they did not realize the reusable suborbital vehicle itself could have been profitable.

 They were regarded as just demonstrators to do experiments on. In point of fact both the X-33 and the suborbital upgrade of the DC-X, known as the DC-Y, could have cut costs and have been profitable as reusable first stages. This could have been done 15 years ago as SpaceX is doing now.

 The key fact is if these are only needed to be first stages they don't need all the extreme weight saving steps that doomed these programs when they were only thought to be demonstrators for a SSTO.

 See the argument here:

DARPA's Spaceplane: an X-33 version.

http://exoscientist.blogspot.com/2013/10/darpas-spaceplane-x-33-version.html

 

  Bob Clark

 

 

 

No, DC-X was too small, it couldn't even get to space by itself. However, DC-Y, the planned successor, and made to be intermediate to the SSTO, would havelikely been able to be used for sounding rocket experiments and possibly a small orbital launcher with a 2-stage solid assembly, and an upgraded-thrust 1st stage. None of the SSTO programs got to that point though.

[Emperor of the Titan Squid]

    I am so happy that you started a thread on this! It's my favorite concept! I like this idea, but I suggest a VentureStar heat shield.I think that MURP is a good idea, but hit had a 7 person capacity, so anything else would work.Also there were supposed to be 2 versions, 1 for crew and1 for cargo.Also, are you considering a cargo bay? If so delete it and replace it with a vertically stacked bay.

[sevenperforce]

Yeah, the internal payload bay makes little sense. I really need to do some math to have a better idea of how it can be scaled. 

Most cargo deliverables are on the order of a Dragon V2's mass or greater. So to use the same RLV for crew transfer as for cargo flights, you want a vehicle which can SSTO a manned capsule in its base, stripped-down configuration but can have its thrust and its tankage capacity augmented to lift heavier payloads. 

That's the major advantage of using an open flowpath: you get to play around with the possibility of multiple fuel injection points.