Stratolaunch: General Company and Development Updates and Discussions

[spacenut]

What type rocket and payload is Stratolaunch going to launch first?  A solid booster rocket would be heavy.  A hypergolic would be easier to maintain on the ground before take off (no boil off).  Hydrolox or metholox would possibly require  refrigeration equipment to keep the fuel liquid to avoid excessive boil-off during take off and altitude climbing before release.  Just wondering what the maximum possible payload stratolaunch could achieve, with expendible rocket and reusable space plane or rocket. 

[envy887]

So, I did some calculations for a SSTO based on the Falcon9 upper stage mass ratios. I used that because I had the most solid data for it. I hope others will do similar with other structure/engine/propellant combinations:
Assumptions:
I went ahead and doubled the GLOW for the Falcon 9 upper stage, which results in roughly 222 tons of mass.
I assume a dry mass 13 tons. This assumes 3 MVacs attached to two F9 US oxygen tanks and two F9 US RP1 tanks for a total of 8.5 tons, leaving about 4.5 tons for wing/lifting body, additional support structure, TPS and landing gear.
It may be possible to shave some weight of this by combining the two sets of tanks, but we are having the thing hang horizontally before launch so the extra structure may be needed.
A crew compartment (or capsule) for 3 people with 3 tons gross weight (or an equivalent other payload) seems reasonably doable based on the weight of Dragon or the Apollo command module (we don't need TPS, thrusters, etc).
So the total dry weight plus payload would be 16 tons.
I made the assumption that the MVac can operate at full Isp/thrust at the release altitude. That may not be the case, but I am not sure how much I would have to subtract for that, since I don't know enough about Roc and the proposed launch parameters.
MVac Isp according to SpaceX: 348
T/W ratio at liftoff is 1.5
Entering these assumptions into Strout's DeltaV calculator I get a DeltaV of about 9096.51 m/s.
I am not sure how much Delta V the Roc will provide in the end, but maybe 150 m/s?  So close to 9250 m/s total DeltaV.
With a moderately reduced Isp of 330, I still get a Delta V of 8626 m/s, adding the 150 m/s from Roc, it may just be enough to get back from orbit too...
Please feel free to correct any mistakes I might have made.

MVac will flow sep at 10 km unless you trim the nozzle back to ~120:1. The average I_sp will probably be around 330-335 to that configuration.

[Elmar Moelzer]

MVac will flow sep at 10 km unless you trim the nozzle back to ~120:1. The average I_sp will probably be around 330-335 to that configuration.

Thanks for the info!
I know that B747s that Roc is based on, can climb to about 14,000 meters, but I don't know when it will actually release the space plane (maybe it can go even higher?). But for the sake of the thought exercise, what nozzle expansion ratio can we support at that altitude and how would that affect average Isp (two things I have not figured out how to calculate myself yet)?

[yg1968]

At yesterday's House hearing Acting Administrator Lightfoot was asked whether NASA could use Stratolaunch's capabilities when it comes on-line. Lightfoot answered that NASA has on-ramp clauses in many of its contracts in order to ensure that new entrants (such as Stratolaunch) can be added.

https://forum.nasaspaceflight.com/index.php?topic=44955.msg1796860#msg1796860

[john smith 19]

Good points on both sides of the hydrolox vs other propellants argument.
Gary Hudson and other designers of SSTOs always emphasize the importance of mass fraction for SSTOs over Isp.

Let's unpack the hidden assumptions to that statement. For vertical TO, non airbreathing SSTO concepts mass fraction is vital

Elon Musk made a similar comment on Twitter when people brought up the higher Isp of the hydrolox upper stages on ULA LVs.

And yet when it came time to do US reuse, sorry Kerelox can't cut it. Needs higher Isp after all. 

So, I think there is a lot of valid evidence that mass fraction will help a lot and kerolox systems like the F9 and FH have demonstrated very impressive mass fractions.

Is that because RP1 is a RTP liquid or could that just be any hydrocarbon.

We have yet to see how well Methalox will perform in comparison when BFS/BFR starts flying. We already know the mass fractions for proposed hydrolox SSTOs.

The engine can be tested on the ground. Structures are more prolematical. TPS even more so.

From my personal understanding of things, it looks pretty even among all three. You gain some, you lose some. I would not dare to say that hydrolox is the _only_ option. It certainly does sound feasible, though.
Regarding the _linear_ aerospike engine for the X-33, I remember that it was necessary to be _linear_ because of the shape of the X-33. A more traditionally shaped aerospike or plug should be a lot easier to develop and would probably perform better. Of course high chamber pressures help too.
Whoever is going to develop that "space plane" certainly have their work cut out for them. I don't believe that this is something we can expect to see in the near term.

And you'd be wrong, given that's essentially what BFS has turned into.

The whole rocket ships vs. space planes argument is playing out these days. There are many space plane designs, and so far, they've all either died in the hangar or on the drafting table, or were non competitive.

I am glad that space planes are given a fair chance.  I am not a fan of the concept, but would hate for then to disappear just due to lack of trying.

They won't.  I guarantee at least one of them is going to be flying by the mid to late 2020's.

Flying, maybe.  Competitive? We'll see.

But not for lack of trying, that's the main deal.

Between VG, XCor, VO, dreamchaser, spaceplane, stratolaunch, skylon - we'll see every combination of LV that has a flight portion to it, with every type of propulsion.

So we'll see.


------
ABCD: Always Be Counting Down

Actually you missed the one I was thinking about.

You seem to have forgotten the BFS  is now also a spaceplane. It will be using wings and aerodynamic lift for part of its trajectory.

So yes, we will see how the spaceplane concept works out.

SSTO isn’t impossible. There are multiple ways to achieve it. If someone wants to use airlaunch, though, the case for hydrogen (provided you solve storage issues or can top off from the carrier plane), is better than it is for ground launch.

Expendable SSTO is SUPER easy. FH side booster could do it. Even the original Atlas rocket (over half a century old) was pretty close to it and could do it if fitted with modern engines.

Correct.

The challenges have always been
a) A VTO SSTO has less payload fraction for the same size of vehicle
b) In theory reusability is harder as you take the whole vehicle to orbit.

So people think it's easier to start with a TSTO and evolve it

Like the way SX planned to evolve their ELV into a full reusable RLV for example.

The difference between a Kerelox system and a hydrolox system (say 326s Vs 380s for SSME at SL) is about 16%
The difference between a Hydrolox rocket and an air breathing Hydrolox is more like 3000s Vs 380s IE 689%
larger.

Basically is Hydrolox rocket worth the extra effort? Seems like a lot of hard work for not that much gain.
OTOH Hydrolox air breathing (even over part of the trajectory) makes a huge improvement. Effectively it enables "virtual staging" of the vehicle and a much more relaxed payload fraction (which can be met by structures that are not vertical cylinders).

[CameronD]

The difference between a Kerelox system and a hydrolox system (say 326s Vs 380s for SSME at SL) is about 16%
The difference between a Hydrolox rocket and an air breathing Hydrolox is more like 3000s Vs 380s IE 689%
larger.

Basically is Hydrolox rocket worth the extra effort? Seems like a lot of hard work for not that much gain.
OTOH Hydrolox air breathing (even over part of the trajectory) makes a huge improvement. Effectively it enables "virtual staging" of the vehicle and a much more relaxed payload fraction (which can be met by structures that are not vertical cylinders).

{emphasis mine}  Do you have a source for that?? 

To my knowledge no-one has built and tested an air-breathing hydrolox engine yet.

[Robotbeat]

...
The challenges have always been
a) A VTO SSTO has less payload fraction for the same size of vehicle...

Look, man, I realize you're married to horizontal take-off and airbreathing, but that statement just isn't true.

[envy887]

...
The challenges have always been
a) A VTO SSTO has less payload fraction for the same size of vehicle...

Look, man, I realize you're married to horizontal take-off and airbreathing, but that statement just isn't true.

Compared to TSTO it certainly is lower.

[Robotbeat]

Oh please. He specified VTO, as if horizontal is better in that respect. (It’s not.)

[speedevil]

It depends what you mean by "High Isp" Methalox is "high" Isp compared to Kerolox and SX don't believe they can do full reusability without it.

Or do you know something SX don't?

They have chosen to go with Methalox, rather than Kerolox, for various reasons, including that Mars works better with it, and it's rather cheaper - this doesn't mean they don't believe it can do full reusability. (they may believe that, but it's not proven)

If you replace Raptor with Merlins, using ISP figures of ones flying today, neglecting the minor tank shrink you could do with Kerosene, and calling it a wash because you now need insulation between the tanks, you can get around 50-60 ton to orbit, not 150. (70-90 tons, if you retank in orbit for landing)

That would still be a wholesale complete market-beater, because it can do all of the other things BFR can - except it significantly increases the number of launches you need to get to Mars.

'Mars would be lots more expensive' is quite enough reason to pick it, without needing to believe it wouldn't work fine for earth.

[Robotbeat]

It depends what you mean by "High Isp" Methalox is "high" Isp compared to Kerolox and SX don't believe they can do full reusability without it.

Or do you know something SX don't

Wrong. You keep putting these words in SpaceX’s mouth again and again even when it’s shown that you’re wrong. Stop doing that; it’s called lying.

SpaceX didn’t just say that kerolox could do full reuse, they were actually going to implement it even with the relatively low ISP of a gas generator engine. The reason they didn’t do it is because they judged methane to be better overall (no coking, for instance) and /cheaper/ as well as much easier to make on Mars. Staged combustion engines running at similar pressures for methane and kerosene aren’t very different in terms of Isp (methane is closer to kerosene in Isp than to hydrogen), and kerosene still has a significant density advantage which helps a LOT for SSTO.

Besides, SpaceX doesn’t have direct access to the wisdom of the rocket gods.

[Space Ghost 1962]

Limit yourself to spaceplane engines likely to exist today (at least, although actually obtaining them with reasonable costing is another huge challenge as well!).

There are very few high thrust, reasonable to good iSP ones to begin with. SSME had massive amount of work put into it to make a compact, high reliability, high performance engine. Raptor also claims to be a very compact engine intended for very high performance/reliability/reuse. As far as I know, that's about it.

Yes, you could make other spaceplane engines but it'll take you a fraction to a few billion and 5-10 years to do so.

Start with propulsion that can get reasonable missions to afford that expensive launchpad to payoff. But don't stop there - you'll need optimal structures, tankage, venting, TPS, ... and systems for recovery of all of these. It adds up fast.

Which is why compact propulsion was a "long pole" for Shuttle back in the 1970's. Don't discount it.

Remember, the Orbiter was intended to be "air launched" by a flyback booster originally.

add:
FWIW current Raptor on the test stand isn't a bad choice for a vehicle for Stratolaunch as I look into this more.  It also isn't planned to be used on any vehicle (full scale Raptor for BFR/S).

Given that the AF has provided funds for its development as an US engine, and the potential for operationally responsive launch from an air launch concept, yes, one could serve a profitable launch provider business with a reusable vehicle.

(It's also the case that Paul Allen has been able to talk Elon Musk into SX related opportunities - a rare case to find.)

Also, an autogenously pressurized methalox vehicle is a natural for sustainment as well. (There's been some interesting work done on propane/natural gas as aircraft cargo and propellant, as well as fuel dumping/venting and safety issues.)

It might also be the case that such a small Raptor might not follow with the current reasons for SX to not sell Merlin for other uses, and might more match the BO reasons for selling engines. Remember that Musk is interested in using multiple launch landing sites worldwide for point to point global transport - they might want to encourage more broad acceptance of Raptor in less competitive niches (as Vulcan is a niche from BO's perspective), because it may ease the safety / liability considerations in multiple global legal systems.

[Robotbeat]

A good case for kerosene as an actually superior Fuel for SSTO RLV compared to methane is here:
http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=34919.0;attach=587468

Dunn shows that at similar conditions, methane is just 10s Isp better than kerosene and hydrogen is 75s higher Isp than methane. From that perspective, kerosene and methane are nearly the same. With the (admittedly simplistic) assumptions that Dunn makes, then, kerosene is better for SSTO RLV than methane due to its higher bulk density.

[Elmar Moelzer]

Good points on both sides of the hydrolox vs other propellants argument.
Gary Hudson and other designers of SSTOs always emphasize the importance of mass fraction for SSTOs over Isp.

Let's unpack the hidden assumptions to that statement. For vertical TO, non airbreathing SSTO concepts mass fraction is vital

I was not aware we were talking about air breathing hydrolox now.
For air breathing launchers, all assumptions are hugely different, for any type of fuel. I did not see Stratolaunch make any announcements regarding an air breathing rocket engine/rocket plane, though.

And yet when it came time to do US reuse, sorry Kerelox can't cut it. Needs higher Isp after all. 

have not seen a single quote that it was the Isp of the US that prevented that. IIRC, it was cancelled because they are moving on to BFS/BFR anyway and that is taking all their development from now on.

So, I think there is a lot of valid evidence that mass fraction will help a lot and kerolox systems like the F9 and FH have demonstrated very impressive mass fractions.

Is that because RP1 is a RTP liquid or could that just be any hydrocarbon.

Not sure I understand the question. I only know that RP1 has an impressive mass fraction because of F9.

The engine can be tested on the ground. Structures are more prolematical. TPS even more so.

Not exactly sure what this is referring to. I am saying that we have seen hydrolox SSTO proposals like the X-33 and we have seen the proposed mass fractions for those. So we can at least assume mass fractions for hydrolox SSTOs based on these.

From my personal understanding of things, it looks pretty even among all three. You gain some, you lose some. I would not dare to say that hydrolox is the _only_ option. It certainly does sound feasible, though.
Regarding the _linear_ aerospike engine for the X-33, I remember that it was necessary to be _linear_ because of the shape of the X-33. A more traditionally shaped aerospike or plug should be a lot easier to develop and would probably perform better. Of course high chamber pressures help too.
Whoever is going to develop that "space plane" certainly have their work cut out for them. I don't believe that this is something we can expect to see in the near term.

And you'd be wrong, given that's essentially what BFS has turned into.

Not sure which of the statements above you think is wrong also not sure what the BFS has to do with an air launched space plane.

You seem to have forgotten the BFS  is now also a spaceplane. It will be using wings and aerodynamic lift for part of its trajectory.

It is still a VTOL. The "wings" are very small and to my understanding more intended as control surfaces to help with keeping the thing oriented, particularly since the cargo is on top, making it rather top heavy.

The challenges have always been
a) A VTO SSTO has less payload fraction for the same size of vehicle

I am not sure about that. Wings add a lot of dead weight.

The difference between a Kerelox system and a hydrolox system (say 326s Vs 380s for SSME at SL) is about 16%
The difference between a Hydrolox rocket and an air breathing Hydrolox is more like 3000s Vs 380s IE 689%
larger.

Basically is Hydrolox rocket worth the extra effort? Seems like a lot of hard work for not that much gain.
OTOH Hydrolox air breathing (even over part of the trajectory) makes a huge improvement. Effectively it enables "virtual staging" of the vehicle and a much more relaxed payload fraction (which can be met by structures that are not vertical cylinders).

That air breathing again. I don't think VG is going to develop an air breathing rocket engine any time soon.
That to my understand is a lot more complicated than a regular rocket engine and would take much longer to develop.

[envy887]

A good case for kerosene as an actually superior Fuel for SSTO RLV compared to methane is here:
http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=34919.0;attach=587468

Dunn shows that at similar conditions, methane is just 10s Isp better than kerosene and hydrogen is 75s higher Isp than methane. From that perspective, kerosene and methane are nearly the same. With the (admittedly simplistic) assumptions that Dunn makes, then, kerosene is better for SSTO RLV than methane due to its higher bulk density.

I wonder if you could get RL-10 to run on MAPP gas and LOX. That would almost triple the thrust, which eliminates the main disadvantage of RL-10 and LH2 in general. And even in a mass constrained near-SSTO airdrop this offers reasonably close to LH2 performance. 6 or 7 tonnes payload to LEO looks feasible.

[Hobbes-22]

What type rocket and payload is Stratolaunch going to launch first? 

As things stand now, an Orbital Pegasus is most likely.

[Patchouli]

Well they J2-X is just sitting around...

It would be a good application for it though they might need a run a compromise style nozzle like the SSME.
TAN could be a good cheat to solve flow separation and add a little more thrust early on or go with an extendable nozzle extension like the RL-10B2.

Now would it be cost effective is another matter as how much was the J-2X supposed to cost when mass produced?

The BE-3U might be better even though you need 3 of them to equal 1J-2X.

[john smith 19]

They have chosen to go with Methalox, rather than Kerolox, for various reasons, including that Mars works better with it,

Weird that. Given Musks endgame has always been Mars, and Mars has no oil to make RP1 out of.
Then again Merlin1a used ablative cooling. The poster boy for single use, weapon system or WS derived LV's.  . I'd love to know where the idea that ablative cooling spelt "easy reusability" came from.

and it's rather cheaper - this doesn't mean they don't believe it can do full reusability. (they may believe that, but it's not proven)

I think they do believe it is needed to do full reusability, because Musk said as much in 2014 at MIT.

No, they have not proved it, but they proved (to their own satisfaction) that they can't make an LOX/RP1 US that can deliver an economic (IE a capability that's big enough to sell to customers) payload to LEO, or GTO.

Oh please. He specified VTO, as if horizontal is better in that respect. (It’s not.)

No I specified it because when people say SSTO they are usually picturing either DC-X or a squat, low AR Phillip Bono design with a plug nozzle engine.

There are a lot of assumptions when people use the term "SSTO" without specifying what they mean.

And you should know by now what happens when you assume things.

Well they J2-X is just sitting around...

Ah yes.

Gas chamber tap off. Unlimited starts. Fast child down.

Oh. You mean the new J2-X.

The thing that's basically a human rated RS68 because it's now got a J2 turbo pump design on it?
Yes that could use a test flight.

I wonder if you could get RL-10 to run on MAPP gas and LOX. That would almost triple the thrust, which eliminates the main disadvantage of RL-10 and LH2 in general. And even in a mass constrained near-SSTO airdrop this offers reasonably close to LH2 performance. 6 or 7 tonnes payload to LEO looks feasible.

Probably. Over the years RL10's have been run on a lot of propellants. FLOX for oxidizer. Methane for fuel and IIRC several others.

TBH I noticed most hydrocarbon fuels (Methane, Propane, Butane) are pretty similar except Propyne (the key part of MAPP gas). The strained bonds seem to be what helps it's performance. IIRC JP10 (used to fuel cruise missiles) also has these, but as a liquid won't work with the RL10 drive system. Obviously tarring up the cooling channels may be an issue.

[john smith 19]

I was not aware we were talking about air breathing hydrolox now.
For air breathing launchers, all assumptions are hugely different, for any type of fuel. I did not see Stratolaunch make any announcements regarding an air breathing rocket engine/rocket plane, though.

Again it's the implicit assumptions people make when they talk about SSTO. IRL what 99% of people are talking about is VTO Rocket driven SSTO. Rocket based SSTO is what  you're talking about isn't it?

have not seen a single quote that it was the Isp of the US that prevented that. IIRC, it was cancelled because they are moving on to BFS/BFR anyway and that is taking all their development from now on.

Check Musk's appearance at MIT in 2014.

So, I think there is a lot of valid evidence that mass fraction will help a lot and kerolox systems like the F9 and FH have demonstrated very impressive mass fractions.

One is a truism and the other is an observation. It's possible to design a cylindrical object with a good mass fraction. A soda can weighs 11g and holds a contents about 330g. It can support 9 furth cans on top of itself without being pressurized. The surprise is not that it is possible.

The surprise is that others don't do it.

Not sure I understand the question. I only know that RP1 has an impressive mass fraction because of F9.

Are you saying RP1 is exceptional, or could it be any hydrocarbon that can give a good mass fraction?

Not sure which of the statements above you think is wrong also not sure what the BFS has to do with an air launched space plane.

You don't seem to think anyone is developing a spaceplane. BFS is a spaceplane and SX are developing. So you are wrong. You're right it won't be easy.

It is still a VTOL. The "wings" are very small and to my understanding more intended as control surfaces to help with keeping the thing oriented, particularly since the cargo is on top, making it rather top heavy.

I keep hearing that but have you noticed the size of the figure Musk includes in the pictures? It's tiny.
You can call them "control surfaces" but I don't expect they will be getting any smaller. I suspect they will get bigger but we'll see.

The challenges have always been
a) A VTO SSTO has less payload fraction for the same size of vehicle

I am not sure about that. Wings add a lot of dead weight.

That would be against a VTO rocket. Again, it's about the implicit assumptions that people make when they talk about SSTO's.

That air breathing again. I don't think VG is going to develop an air breathing rocket engine any time soon.
That to my understand is a lot more complicated than a regular rocket engine and would take much longer to develop.

Stratolaunch is not part of Virgin Galactic. It is a subsidiary of Paul Allan's company "Vulcan."

[hkultala]

[offtopic]

It depends what you mean by "High Isp" Methalox is "high" Isp compared to Kerolox

.. but low isp compared to hydrolox.

In any meaningful context, it's medium isp.

and SX don't believe they can do full reusability without it.

Total crap.

SpaceX has NEVER said they cannot do it, they have multiple times said they COULD do it but they have clearly said they don't WANT to do it because it would cost them a lot of engineering resources and they want to concentrate all their engineering resources to their next-gen system which will do it with better margin.

Or do you know something SX don't?

So, now you are trying to use "appealing to authority" argument by using a claim the authority NEVER SAID.

Please, stop this crap.

[/offtopic]