SSTOs galore

[KerikBalm]

yes, aerospikes are good

that doesn't make SSTO chemical rockets good...

[sevenperforce]

3 hours ago, KerikBalm said:

still won't survive re-entry... making it a disposable rocket with a terrible payload

It could burn up to orbital velocity, MECO, release payload, burn retrograde back down to a safe re-entry speed, and then re-enter for a high-speed landing a la JCSAT-14. 

Of course payload might be negative. 

The empty first stage masses 22.2 tonnes and needs at least 20 tonnes of reserve fuel for re-entry burn and landing burn from a MECO of 2,321 m/s. That's from the JCSAT-14 hot landing. By the rocket equation, a burn from 2,321 m/s to 7,800 m/s and back down again (i.e., zero payload) requires almost 11 km/s of dV. With a terminal mass of 42.2 tonnes, the Falcon 9 first stage would need 1,516 tonnes of propellant left...more than the entire propellant capacity of Falcon Heavy.

Even with an aerospike engine to push the vacuum ISP to 348 seconds, it would still require 1,019 tonnes of propellant to come back. 

Of course, if you are talking about expending an end-of-life Falcon 9 first stage, then with altitude compensation you could get a good solid 3 tonnes of payload to orbit.

Edited May 20, 2016 by sevenperforce

[Kryten]

Very unlikely to be worth the effort to support a new configuration for a smaller market.

[Thor Wotansen]

On a slightly different note, wasn't the Buran originally designed to be launched from the back of the Antonov An 225?

[sevenperforce]

2 hours ago, Kryten said:

Very unlikely to be worth the effort to support a new configuration for a smaller market.

Oh, I agree absolutely. Not worth it at all. 

People make too much of Elon saying that the first stage can SSTO by itself. Sure, it can, but with negligible payload. I wanted to run the numbers to see.

It wouldn't make sense for SpaceX to do this, anyway. If they have an end of life booster they will either cannibalize it for parts or they will launch it on an expendable ordinary mission. 

[Nibb31]

5 hours ago, Thor Wotansen said:

On a slightly different note, wasn't the Buran originally designed to be launched from the back of the Antonov An 225?

No, that wouldn't even be remotely possible. The Antonov was for transporting the orbiter, just like NASA's 747 SCA.

[Ravenchant]

11 hours ago, Thor Wotansen said:

On a slightly different note, wasn't the Buran originally designed to be launched from the back of the Antonov An 225?

You're thinking of MAKS

[Thor Wotansen]

47 minutes ago, Ravenchant said:

You're thinking of MAKS

yeah that

[wumpus]

21 hours ago, fredinno said:

Why would a atmosphere+ H2 work better? Lazer+H2 has higher ISP, and you can pump lasers at it for far longer on its orbit.

Atmosphere+(fuel used by X-43A) had an effective ISP of over 1500 at mach 9.6 (3000km/s) and an effective ISP of 2500 at 2000km/s.  I'm fairly sure this includes the exhaust momentum of the air without counting against the mass of the air.  H2 will typically have an ISP similar to a NERVA (escape dynamics claims between 750-850, just like a NERVA).

Obviously, once the airbreather ran out of air, the laser would be superior.  This is assuming the laser can maintain the needed temperature.  This isn't nearly as clear as the laser's heating efficiency is much lower than while the spacecraft is ascending.  I strongly suspect early laser launchers will sacrifice ISP at higher elevations to launch a larger spacecraft relative to the power of the laser needed for maximum ISP all the way up.  This is a bit of a problem, as the US Navy is pouring millions of dollars into a program that might generate a 1MW laser by 2025, and presumably need only fire that laser for ms at a time (escape dynamics planned on 200MW for roughly the duration of the flight).

Finally, there is that whole issue of what you are optimizing.  A KSP player quickly learns that raising the ISP of the bottom has a linear effect on the overall rocket (because the upper stages contain effective "dry weight").  Raising the ISP of the last stages has an exponential effect on the overall rocket.  However, if you are at a point where fuel usage begins to matter for launches (airlines are obviously here, space has a looong way to go), increasing first stage efficiency still has a massive effect on the fuel consumed (largely because it is 70-90% of the overall mass).

http://escapedynamics.com/wp-content/uploads/2015/05/Escape-Dynamics-External-Propulsion-WP.pdf

(hopefully this like will last a little while, less sure since they closed up shop).

PS:

21 hours ago, fredinno said:

Probably an admission that investing heavily in those kinds of RLVs (TSTO or SSTO) doesn't make much economic sense right now. SpaceX and Blue Origin only bothered with reuse because it was their dreams- a good thing, but not good for profits or economy.

SpaceX has three extremely expensive boosters in a warehouse thanks to reuse (presumably somewhere between $50-60M worth of rocket).  Also a cynic would point out that the "dreams" those companies run on likely allow considerably reduced salaries and hiring more capable employees as well.  It may have been a net win just in that even if those boosters are launched "at recovery cost".

The other thing to notice is that SpaceX only attempts to recover the booster, and Blue Origin (and Virgin Galactic) don't even go that high/fast.  NASA managed to recover the Shuttle from full orbit (with the main engines) and that managed to be the most expensive* way to space (per pound/for anything medium lifter and up) ever to fly.  For anyone declaring re-use 'trivial' once you've recovered the (orbiting) vehicle, first explain to NASA how they could have made shuttle flights cheap.

* didn't bother to check.  It was stupid expensive, and NASA wouldn't let you deliver anything to space without 7 astronauts tagging along for the ride.

Edited May 21, 2016 by wumpus
noticed the swipe at re-use.

[Exoscientist]

21 hours ago, sevenperforce said:

Oh, I agree absolutely. Not worth it at all. 

People make too much of Elon saying that the first stage can SSTO by itself. Sure, it can, but with negligible payload. I wanted to run the numbers to see.

It wouldn't make sense for SpaceX to do this, anyway. If they have an end of life booster they will either cannibalize it for parts or they will launch it on an expendable ordinary mission. 

 

  What do you estimate it to be? Some estimates put it at 2 metric tons, hardly negligible.

   Bob Clark

[Nibb31]

6 hours ago, Exoscientist said:

 

  What do you estimate it to be? Some estimates put it at 2 metric tons, hardly negligible.

   Bob Clark

Once you add a fairing and a spacecraft adapter, there wouldn't be much left out of those 2 tons. And you'll be throwing away a whole first stage with 9 Merlins.

[Jovus]

On 5/21/2016 at 5:54 PM, wumpus said:

The other thing to notice is that SpaceX only attempts to recover the booster, and Blue Origin (and Virgin Galactic) don't even go that high/fast.  NASA managed to recover the Shuttle from full orbit (with the main engines) and that managed to be the most expensive* way to space (per pound/for anything medium lifter and up) ever to fly.  For anyone declaring re-use 'trivial' once you've recovered the (orbiting) vehicle, first explain to NASA how they could have made shuttle flights cheap.

* didn't bother to check.  It was stupid expensive, and NASA wouldn't let you deliver anything to space without 7 astronauts tagging along for the ride.

Hey now. I'm no fan of the STS program, but the real well-and-truly expensive thing about it wasn't re-use per se, but rather the fact that the STS was engineer-retention program with this minor problem of Congress thinking it was a space program.

With an actual focus on cost-saving and economic re-use, the Shuttle could have been made much cheaper to fly. With an actual design sticking to the original pitched-to-Congress-as-reusable project design document, it would have been much cheaper still.

Don't get me wrong. I'm no Shuttle fanboy. It still would have been worse than a traditional rocket a la the Soyuz. But don't you think pulling out the STS program as a model of economic re-usability of space hardware is a little unfair? At the very least, NASA's incentives are the exact opposite of 'make a profit'.

On 5/21/2016 at 0:41 AM, Exoscientist said:

 

  What do you estimate it to be? Some estimates put it at 2 metric tons, hardly negligible.

   Bob Clark

Assuming that's correct, the payload fraction would be somewhere around 0.00002%. Hardly worth the fuss, don't you think?

[fredinno]

On 2016-05-20 at 1:12 PM, Exoscientist said:

  The Vega is also expendable and costs $45 million for a payload to LEO of only 2,500 kg, yet still has a market.

  But as I said there are many ways of accomplishing altitude compensation that would MAJORLY increase the payload to LEO. I have discussed how much more it could be but nobody believes it. Try the calculation yourself: use the rocket equation or one of the launch simulators to see how much is the payload when the vacuum Isp of the Merlins on the F9 first stage is increased from 311 s to 342 s.

    Bob Clark

Yeah, and that market is a niche market right now, and is set to launch 3-4 times a year only. And that's the bigger player in that market.

 

And altitude compensation is great- but the problem is development costs. It's going to be very expensive, and for all that trouble, just do a TSTO. Engines are the most expensive part of a rocket anyways, and adding an air intake is going to push complexity up into the sky.

[fredinno]

On 2016-05-20 at 2:26 PM, sevenperforce said:

Of course, if you are talking about expending an end-of-life Falcon 9 first stage, then with altitude compensation you could get a good solid 3 tonnes of payload to orbit.

But altitude compensation would require a new F9 booster....

On 2016-05-21 at 7:31 PM, sevenperforce said:

Oh, I agree absolutely. Not worth it at all. 

People make too much of Elon saying that the first stage can SSTO by itself. Sure, it can, but with negligible payload. I wanted to run the numbers to see.

It wouldn't make sense for SpaceX to do this, anyway. If they have an end of life booster they will either cannibalize it for parts or they will launch it on an expendable ordinary mission. 

23 hours ago, Nibb31 said:

Once you add a fairing and a spacecraft adapter, there wouldn't be much left out of those 2 tons. And you'll be throwing away a whole first stage with 9 Merlins.

There are probably a few missions SpaceX might want to do with a SSTO F9 with 1.5T payload, actually- Oneweb and SpaceX's nominal internet sats would come to mind. Unfortunately, the R+D to make it happen probably more justifies a F1 revival- at least then, they can make a "F1 Heavy" with Delta II payload, and add F1 LRBs to F9, Atlas V style. Assuming such a demand arises. Also, a F1 revival would feature a partially reusable F1- as planned.

 

55 minutes ago, Jovus said:

Hey now. I'm no fan of the STS program, but the real well-and-truly expensive thing about it wasn't re-use per se, but rather the fact that the STS was engineer-retention program with this minor problem of Congress thinking it was a space program.

With an actual focus on cost-saving and economic re-use, the Shuttle could have been made much cheaper to fly. With an actual design sticking to the original pitched-to-Congress-as-reusable project design document, it would have been much cheaper still.

Don't get me wrong. I'm no Shuttle fanboy. It still would have been worse than a traditional rocket a la the Soyuz. But don't you think pulling out the STS program as a model of economic re-usability of space hardware is a little unfair? At the very least, NASA's incentives are the exact opposite of 'make a profit'.

The shuttle was a bad design overall, designed for 50 man space bases that never happened. Even a efficient version would have never gotten enough money to build the proposed 2-stage reusable version. The Shuttle would be a completely different design from what we got.

Which is why without the post-Apollo over-optimism and management that favored the Shuttle solution before anything else (and pork), NASA would probably have started out with something like an unmanned StarClipper.

 

Or just sea land ELV booster stages, or a reusable winged Saturn IB booster. That would work too.

[Jovus]

11 minutes ago, fredinno said:

The shuttle was a bad design overall, designed for 50 man space bases the KH-9 Hexagon that never happened. Even a efficient version would have never gotten enough money to build the proposed 2-stage reusable version. The Shuttle would be a completely different design from what we got.

FTFY. But yes, absolutely.

[tater]

Dragging 84 metric tons of Orbiter to space to carry 25 tons of actual cargo to orbit made no sense whatsoever. 

[wumpus]

9 hours ago, Jovus said:

With an actual focus on cost-saving and economic re-use, the Shuttle could have been made much cheaper to fly. With an actual design sticking to the original pitched-to-Congress-as-reusable project design document, it would have been much cheaper still.

Even ignoring the extra dry weight of the shuttle (roughly assuming five times the cargo capacity), it still wouldn't be a big cost savings to go reusable.  And many of the "originally pitched to congress" plans were explicitly TSTO (instead of a half-stage of SRBs plus the main stage, with a tiny circularization engine at the end).

Considering the "just into space" programs (X-15, Space ship  one, Blue origin, and Falcon 9) all appear to be reusable on reasonable budgets and all avoided reusing orbital parts and the single one that didn't (the Shuttle) had out of control costs.  While it may be that having out of control spending lead to an attempt to recover the orbiter, it didn't work well in controlling costs.

[Jovus]

You say all that like you think I disagree with you.

[RenegadeRad]

1 hour ago, Jovus said:

You say all that like you think I disagree with you.

Welcome to the internet...

[Exoscientist]

11 hours ago, Jovus said:

Assuming that's correct, the payload fraction would be somewhere around 0.00002%. Hardly worth the fuss, don't you think?

 If the payload of the F9 first stage as an SSTO is 2.3 metric tons then the payload fraction would be 2.3/442.3= 0.005, or 0.5%, based on an estimated gross mass of the F9 first stage by itself of 440 metric tons. Common payload fractions of orbital launchers are in the 3% to 4% range. 

 But as I said SSTO's get their best performance when using altitude compensation, such as the aerospike. This can increase the payload multiple times. It may in fact be in the payload fraction range of commonly in use multistage rockets. 

  Bob Clark

 

Edited May 23, 2016 by Exoscientist

[wumpus]

On 5/21/2016 at 0:54 PM, wumpus said:

Atmosphere+(fuel used by X-43A) had an effective ISP of over 1500 at mach 9.6 (3000km/s) and an effective ISP of 2500 at 2000km/s.  I'm fairly sure this includes the exhaust momentum of the air without counting against the mass of the air.  H2 will typically have an ISP similar to a NERVA (escape dynamics claims between 750-850, just like a NERVA).

The writeup* on today's Indian space launch at least mentions plans for a RAMJET/SCRAMJET launcher for their "spaceplane" (for more Shuttle types of "spaceplane").  No idea if this has gone past powerpoint, but at least somebody is thinking about it.

http://arstechnica.com/science/2016/05/indias-shuttle-like-reusable-spaceplane-makes-its-first-test-flight/

[still looking for the KSP forum thread on the launch].

[Emperor of the Titan Squid]

 

 

On 5/18/2016 at 5:03 PM, Kryten said:

EDIT: Heck, even Jess Sponable, one of the guys heading DC-X and responsible for their straight-to-SSTO stance, is now running a flyback/boostback TSTO booster program, XS-1.

Thats the way to be going.

[fredinno]

On 2016-05-23 at 11:23 PM, Jovus said:

FTFY. But yes, absolutely.

It was ORIGINALLY, as in that was how it was pitched to Congress.

But yeah, it basically devolved into the KH-9 purpose. But the SHuttle design was HEAVILY influenced under the assumption of both.

On 2016-05-23 at 7:58 AM, wumpus said:

Even ignoring the extra dry weight of the shuttle (roughly assuming five times the cargo capacity), it still wouldn't be a big cost savings to go reusable.  And many of the "originally pitched to congress" plans were explicitly TSTO (instead of a half-stage of SRBs plus the main stage, with a tiny circularization engine at the end).

Considering the "just into space" programs (X-15, Space ship  one, Blue origin, and Falcon 9) all appear to be reusable on reasonable budgets and all avoided reusing orbital parts and the single one that didn't (the Shuttle) had out of control costs.  While it may be that having out of control spending lead to an attempt to recover the orbiter, it didn't work well in controlling costs.

That was because at the time of its creation, reusing the "orbital parts" was easier, otherwise, you needed jet engines to do precision landings.

Also, you compared apples (3 suborbital spaceships) to oranges (Shuttle.) That did a lot of damage to your net argument.

On 2016-05-23 at 9:54 AM, Exoscientist said:

 If the payload of the F9 first stage as an SSTO is 2.3 metric tons then the payload fraction would be 2.3/442.3= 0.005, or 0.5%, based on an estimated gross mass of the F9 first stage by itself of 440 metric tons. Common payload fractions of orbital launchers are in the 3% to 4% range. 

 But as I said SSTO's get their best performance when using altitude compensation, such as the aerospike. This can increase the payload multiple times. It may in fact be in the payload fraction range of commonly in use multistage rockets. 

  Bob Clark

 

But can it be reusable? A non-reusable SSTO is pointless...

On 2016-05-23 at 0:05 PM, wumpus said:

The writeup* on today's Indian space launch at least mentions plans for a RAMJET/SCRAMJET launcher for their "spaceplane" (for more Shuttle types of "spaceplane").  No idea if this has gone past powerpoint, but at least somebody is thinking about it.

http://arstechnica.com/science/2016/05/indias-shuttle-like-reusable-spaceplane-makes-its-first-test-flight/

[still looking for the KSP forum thread on the launch].

India doesn't take its manned space efforts seriously, unsurprisingly. And this is more like an X-plane, than anything else. Still cool tho.

[Exoscientist]

On May 26, 2016 at 0:02 PM, fredinno said:

But can it be reusable? A non-reusable SSTO is pointless...

   Altitude compensation such as the aerospike is really important for SSTO's. It can increase payload multiple times. Most people don't realize how large can be the payload increase because they haven't done the calculation. They see that the alt. comp. vacuum ISP at 342 s is only 10% higher than the standard non alt. comp. case at 311 s, so they think the improvement in payload is some similar small amount, say, from 2,000 kg to LEO to 2,200 kg. 

 No! Because the rocket equation is exponential the payload becomes several times higher. So much higher in fact that even with the extra mass required for reusability, the payload is still high to LEO.

  Bob Clark

[fredinno]

8 hours ago, Exoscientist said:

   Altitude compensation such as the aerospike is really important for SSTO's. It can increase payload multiple times. Most people don't realize how large can be the payload increase because they haven't done the calculation. They see that the alt. comp. vacuum ISP at 342 s is only 10% higher than the standard non alt. comp. case at 311 s, so they think the improvement in payload is some similar small amount, say, from 2,000 kg to LEO to 2,200 kg. 

 No! Because the rocket equation is exponential the payload becomes several times higher. So much higher in fact that even with the extra mass required for reusability, the payload is still high to LEO.

  Bob Clark

You also didn't account for the extra mass of the intake, and the higher strucutral mass and less efficient profile due to having to use the atmopshere as much as possible...

 

But in any case, alt. compensation with a SSTO is still stupid, since on a TSTO,  you can have a even smaller, cheaper rocket using alt. compensation.