SpaceShipThree Question: Could a 2-3 engine design get us to LEO?

[mlorrey]

Since The National Geographic special wasn't in Canada I watched the 2 preview clips on the NatGeo channel..and this video shows, at a 1:30 in , a concept i was surprised of.  They spent money making the clip but I hope they weren't serious in the design.  Basically show SS2 in orbit on a space station/hotel...

Nah, they weren't engineering serious.  Remember that this clip was designed as a drop-jaw illustration for the narration.  One of the objectives of it was doubtless to include objects that the audience would recognise to increase the sense that it was something "just around the corner".  SS2, which is inaccurately viewed as a spacecraft rather than an extreme-altitude rocket-plane (basically a passenger version of X-15), fitted in with those marketing requirements perfectly.

You can be sure that NatGeo's CGI subcontractors had no idea of the engineering and scientific challenges.  Their objective was art, not technical accuracy.

Yeah, firstly, you would need to give SS2 a new thermal protection system that is orbital return capable. The current TPS is most decidely NOT. This will add mass. Secondly, you will need to change fuels. Probably a LOX/Methane combination, or LOX methylacetylene, something along those lines.
Then you will need a stage behind the SS2 (lets call it a 2.9 or so)... that will also be liquid fueled. Cause SS2 cannot go anywhere near orbit on its own, even with a change in fuels.
All this will add a lot of mass to the vehicle, so you'll need WK2 to bulk up to a WK3.

[mmeijeri]

Secondly, you will need to change fuels. Probably a LOX/Methane combination, or LOX methylacetylene, something along those lines.

Or kerosene/peroxide like Black Horse. Easier to transfer in flight, which removes much of the penalty of wings and landing gear.

[Eerie]

I`d like to see something like VentureStar. Huge aerodynamic fuel tank with wings and some payload. Possibly with a horizontal take-off.

[kkattula]

You guys have depressed me.

I don't see people wanting to ride to space on a vertical rocket.

Is there any hope for Scaled future designs carrying people to orbit?

You might want to take a look at Skylon http://www.reactionengines.co.uk/skylon.html

If the Sabre engine works as advertised, and they get sufficient funding, it could have a passenger capability in 10 to 15 years.

[tobi453]

Hybrids have neither the mass fraction nor the Isp you'd want in order to get to LEO.

Hybrids have a better Isp than solids.

[HMXHMX]

Hybrids have neither the mass fraction nor the Isp you'd want in order to get to LEO.

Hybrids have a better Isp than solids.

But terrible sliver fractions, which means – and the designs confirm – it will take four stages to get to orbit efficiently.  Neither solids nor hybrids have any role to play in routine, affordable, and safe human space transportation, and Burt has always said that (to paraphrase) it is not worth building SS3 unless it contains real breakthroughs.  I happen to disagree with him on that point, but he recognizes that hybrids won't have a place in such a system.

[mmeijeri]

Neither solids nor liquids have any role to play in routine, affordable, and safe human space transportation

You mean hybrids, right? Are reusable solids inherently uneconomical, or is that just the case if you have to recover them from the sea? I'm thinking of a variant on the GTX+GEM idea. What if instead of expendable/reusable separating boosters, you had an integral solid rocket in your ramjet duct for takeoff, like some missiles? Just a wild idea.

[docmordrid]

Hopefully Reaction Engine's SABRE jet/rocket hybrid will work and fill that breakthrough requirement. Tests of a key component, the intake precooler, are scheduled for next summer and should clarify its status.

[HMXHMX]

Neither solids nor liquids have any role to play in routine, affordable, and safe human space transportation

You mean hybrids, right? Are reusable solids inherently uneconomical, or is that just the case if you have to recover them from the sea? I'm thinking of a variant on the GTX+GEM idea. What if instead of expendable/reusable separating boosters, you had an integral solid rocket in your ramjet duct for takeoff, like some missiles? Just a wild idea.

Sorry, you are of course correct.  I've edited the post.  Fingers outrunning brain...

Personally, I believe solids are inherently uneconomical.  First, the propellant costs at least ten times more than liquid fuels of choice, and second, the safety and handling, weight of transportation issues, etc., all make solids unattractive for any low-cost transportation system.  Solids excel at t/w, of course, and even aircraft can benefit from that, but you notice how infrequently we now use such a technology in the RATO role.  There's good reasons why we don't.

[Danderman]

This brings me back to the question of why jet engines aren't used as "Strap-on" boosters for small orbital launchers, like Falcon 1. With a dry weight of a ton or so, and an incredible ISP, a cheap surplus engine like the F-100 should be ideal as a booster for the first 60 seconds or so of flight.

[mmeijeri]

Personally, I believe solids are inherently uneconomical.

Can you expand on how this differs from the economics of solids on EELVs? I understand you don't count EELVs as a low-cost transportation system, but here the solids do appear to be cost effective.

[Lars_J]

This brings me back to the question of why jet engines aren't used as "Strap-on" boosters for small orbital launchers, like Falcon 1. With a dry weight of a ton or so, and an incredible ISP, a cheap surplus engine like the F-100 should be ideal as a booster for the first 60 seconds or so of flight.

Thrust matters at liftoff. Little else. And no jet engine can match a rocket in T/W ratio. So you are better off adding a solid or liquid booster rocket instead of a jet engine.

[Danderman]

This brings me back to the question of why jet engines aren't used as "Strap-on" boosters for small orbital launchers, like Falcon 1. With a dry weight of a ton or so, and an incredible ISP, a cheap surplus engine like the F-100 should be ideal as a booster for the first 60 seconds or so of flight.

Thrust matters at liftoff. Little else. And no jet engine can match a rocket in T/W ratio. So you are better off adding a solid or liquid booster rocket instead of a jet engine.

Cost matters, too. Solids are relatively expensive, and generate significant risks.

[HMXHMX]

This brings me back to the question of why jet engines aren't used as "Strap-on" boosters for small orbital launchers, like Falcon 1. With a dry weight of a ton or so, and an incredible ISP, a cheap surplus engine like the F-100 should be ideal as a booster for the first 60 seconds or so of flight.

It's all down to flight rate.  In the past, people have made a decent economic case for "POGO"-style jet-assist but not unless flight rate is in the RLV range of 30-40 per year.  Of course, WK2 is using jet engines for just this purpose. 

And RASCAL explored a version of the approach as well.

[Jim]

This brings me back to the question of why jet engines aren't used as "Strap-on" boosters for small orbital launchers, like Falcon 1. With a dry weight of a ton or so, and an incredible ISP, a cheap surplus engine like the F-100 should be ideal as a booster for the first 60 seconds or so of flight.

Thrust matters at liftoff. Little else. And no jet engine can match a rocket in T/W ratio. So you are better off adding a solid or liquid booster rocket instead of a jet engine.

Cost matters, too. Solids are relatively expensive, and generate significant risks.

inexpensive in a non reusable strapon use.

[HMXHMX]

Personally, I believe solids are inherently uneconomical.

Can you expand on how this differs from the economics of solids on EELVs? I understand you don't count EELVs as a low-cost transportation system, but here the solids do appear to be cost effective.

EELV solids are one of the more expensive parts of the stack now. The real reason they were used was to allow a smooth gradation in payload capability, but at the time that decision was made in the mid 1990s, the cost was several fold less than today.  I expect, based on my knowledge of the current decision process (which I can't elaborate due to NDAs), the decision would be made differently if ULA was starting over today.

But we were speaking of SpaceShipThree.  I know the goals for that future speculative capability aim at cost per flight and cost per pound much, much lower than EELVs.

[mmeijeri]

inexpensive in a non reusable strapon use.

Are you disagreeing with HMXHMX on this?