Author Topic: Stratospheric-Airship-Assisted Orbital Payload Launching System  (Read 8600 times)

Online envy887

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Firstly, I should put a note here that this is more a conceptual representation than a detailed design.

Secondly, SLSS, as the third word of its name (Suborbital) states,  doesn't reach orbital speed. For example, in a sample simulation for regional flight profile, SLSS reaches around 15 Mach speed and 112 km altitude at burn-out.

Thanks for your interest and question!

1 - the first time you mentioned SLSS was in this post in reply to mine, so how was I supposed to know it's suborbital?

2 - actually, this is quite confusing, as the other name (your forum nickname) clearly has the word ORBITAL.


3- so, is it ORBITAL or SUBorbital?

4 - if itīs ORBITAL, how can it achieve a 30 km/s delta-v? Fuel tanks seem undersized by an order of magnitude at least.

The spaceship in this concept is suborbital, with a expendable orbital upper stage.

It's basically XS-1, but launching from a giant balloon.

Online envy887

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Aye, the only meaningful advantage of launching from altitude is the ability to use near-vacuum-optimized engines from the start
Are there any advantages to having a much more benign aerodynamic environment (e.g., far lower max Q)?  Would that allow a lighter structure for the actual vehicle, and thus better performance?  If one doesn't have to worry about dense atmosphere, and thus streamlining, does that allow different form factors for the vehicle rather than a slender tube?

There is a fairly large advantage, but only in one area with its own distinct issues: Small launchers.  The smallest launcher that's feasible from the ground is around 10 tons.

Let's give a hypothetical 30 ton 2-stage launcher a 1% payload mass fraction: It can launch 300kg to space.  This isn't very bad - there are satellites in this size range which will pay some money for launch.  Now scale that down by a factor of 10.  A 3 ton 2-stage launcher suffers on a number of metrics that we can fix - Miniaturizing electronics and guidance and comms, a number of metrics that are inherently difficult - working with increasingly thin-walled pressure vessels, and some things we just can't touch - far proportionally greater aerodynamic losses, and thus (because greater aerodynamic force necessitates greater structural strength for the same velocity) a greater mass loss to structural reinforcement, and also a larger dV need & thus wet:dry ratio.  This extends the amount of propellant that needs to be carried, and these effects compound on each other relentlessly.  Long story short: You don't get a 1% payload mass fraction (30kg) out of a 3 ton vehicle of similar design.  Nowhere near.  More likely you'll just never get any kind of payload to orbit.  Somewhere a bit under 10 tons, depending on what tech you use, the aerodynamic-related losses run asymptotic and you just can't make an orbital vehicle that launches from the ground.

You can make one, though, that launches from somewhere above most of the atmosphere.  If you don't have to deal with most of the atmosphere, you never hit the same compounding barriers, and you can scale that 30 ton launcher down to 3 tons without losing all that much payload mass fraction.  You can hypothetically scale things all the way down to launching a single 1U cubesat.

I would note however, that large launchers (EELV class and up) generally don't lose a lot to gravity+drag losses.  The longer the rocket is, the easier it is proportionately to shove through the atmosphere.  So you can't really compete by just using small launchers and upping the volume, without some kind of dramatic advance in mass production.  Alternately, you could find a recurring payload from a paying customer that needs rapid response launches to a number of custom orbits.

But we haven't yet.  And so this sort of idea is not really a feasible business - in a world where there are cheaply reusable first stages and there exist few commercial customers for tiny payloads to custom orbits, a balloon or plane adds so little to the engineering picture that it's difficult to justify those forms of launch.  We're going to be doing mass production of smallsats fairly soon once the LEO comms financing guys feel that launch is cheap enough, but large smallsat dispensers flown from an F9 are likely much cheaper, for a single plane, than custom launches.  Few large constellations will need only one bird per orbital plane.

This proposal is a single-SSME sized LV, so about 100 to 150 tonnes gross liftoff mass. Reduced drag losses are a small advantage at this size, and reduced structural requirements almost trivial since it has to be strong enough to return through the atmosphere from Mach 12.

ISP gain from running the SSME in vacuum or near-vacuum only would be significant, but I can't see how it's worth the major headaches of air-starting a SSME ,or building a huge balloon, or carrying cryo fuels into the stratosphere.

Offline aceshigh

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Firstly, I should put a note here that this is more a conceptual representation than a detailed design.

Secondly, SLSS, as the third word of its name (Suborbital) states,  doesn't reach orbital speed. For example, in a sample simulation for regional flight profile, SLSS reaches around 15 Mach speed and 112 km altitude at burn-out.

Thanks for your interest and question!

1 - the first time you mentioned SLSS was in this post in reply to mine, so how was I supposed to know it's suborbital?

2 - actually, this is quite confusing, as the other name (your forum nickname) clearly has the word ORBITAL.


3- so, is it ORBITAL or SUBorbital?

4 - if itīs ORBITAL, how can it achieve a 30 km/s delta-v? Fuel tanks seem undersized by an order of magnitude at least.

The spaceship in this concept is suborbital, with a expendable orbital upper stage.

It's basically XS-1, but launching from a giant balloon.


but XS-1 is orbital, and it's almost like a payload.

it's launched inside a 60 meters tall Falcon 9 rocket, first stage and second stage reaching 30 thousand km per hour. Then the XS1 is delivered already in orbital velocity.

so, again, how exactly do you plan to reach orbital speeds?


please, describe what is envisioned as the COMPLETE spaceship which will hang below the balloon. What will be it's size? How many stages? What will be it's fuel and amount of fuel? Payload capacity to LEO?

Offline Patchouli

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If you use BE-3 or Merlin it can have engine-out redundancy for most of the flight. And you really don't want to start an RS-25 while dangling on cables under a hydrogen balloon... there is a good reason all air-launch vehicle drop first, then fire. The RS-25 is a difficult engine to start even on the ground. If you drop it, there will be times where a abort on the pad is a lot safer. I'd wager the increased risk of the engine not starting and having to abort is greater than the reduction from having abort capability for a small part of the flight trajectory where the vehicle is within gliding range of a runway.

You still haven't clarified how the suborbital booster returns to a runway. There are a very limited number of sites and launch azimuths where both 1) the ground track of the launch trajectory is acceptable and 2) the booster is within gliding range of a runway when it reenters. Most launch locations and azimuths will require a boostback/diversion burn - but RS-25 cannot RESTART, even if you get it to air-start. You could hot-stage, but that adds a whole 'nother set of complications.

RP-1 freezing isn't really an issue, the booster would need insulated tanks anyway - to prevent solid air buildup on the LH2 tanks.

Again, to convince anyone that air-launch is a good idea, you will need to calculate exactly how much booster cost you are saving by adding the expense of a air-lift stage.
There are airship designs that supposedly can reach altitudes of over 20km which should be high enough you can start off with what would normally be an upper stage engine so why bother dealing with a complex and heavy engine like the RS-25.


but XS-1 is orbital, and it's almost like a payload.

it's launched inside a 60 meters tall Falcon 9 rocket, first stage and second stage reaching 30 thousand km per hour. Then the XS1 is delivered already in orbital velocity.

so, again, how exactly do you plan to reach orbital speeds?


please, describe what is envisioned as the COMPLETE spaceship which will hang below the balloon. What will be it's size? How many stages? What will be it's fuel and amount of fuel? Payload capacity to LEO?

No the XS-1 is a launch vehicle you're thinking the X-37 which is a payload.
« Last Edit: 09/13/2017 01:30 AM by Patchouli »

Online envy887

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RS-25 is a very poor engine choice for this application, IMO. It's not great for the XS-1 application, but at least there it can be ground started.

Offline Archibald

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Quote
It's basically XS-1, but launching from a giant balloon.

and it's a bad idea. The balloon provides little help, yet add complexity.

Online envy887

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Firstly, I should put a note here that this is more a conceptual representation than a detailed design.

Secondly, SLSS, as the third word of its name (Suborbital) states,  doesn't reach orbital speed. For example, in a sample simulation for regional flight profile, SLSS reaches around 15 Mach speed and 112 km altitude at burn-out.

Thanks for your interest and question!

1 - the first time you mentioned SLSS was in this post in reply to mine, so how was I supposed to know it's suborbital?

2 - actually, this is quite confusing, as the other name (your forum nickname) clearly has the word ORBITAL.


3- so, is it ORBITAL or SUBorbital?

4 - if itīs ORBITAL, how can it achieve a 30 km/s delta-v? Fuel tanks seem undersized by an order of magnitude at least.

The spaceship in this concept is suborbital, with a expendable orbital upper stage.

It's basically XS-1, but launching from a giant balloon.


but XS-1 is orbital, and it's almost like a payload.

it's launched inside a 60 meters tall Falcon 9 rocket, first stage and second stage reaching 30 thousand km per hour. Then the XS1 is delivered already in orbital velocity.

so, again, how exactly do you plan to reach orbital speeds?


please, describe what is envisioned as the COMPLETE spaceship which will hang below the balloon. What will be it's size? How many stages? What will be it's fuel and amount of fuel? Payload capacity to LEO?

I'm not the OP, so I'm not sure why you're asking me this. But I would like to see those questions answered. I posed a similar set of questions previously, but they weren't answered.

The OP was apparently going to have a conference presentation yesterday, but the conference was canceled due to Irma.

Offline wilbobaggins

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Sorry for digging up an old thread but am i right in saying the main advantages of air launch are not efficiency gains but;
A Very mobile launch pad (it literally flies)
This allows matching of the target obit's ground track meaning no more waiting days/weeks for launch windows only hours
This also allows launching into any inclination with the same "launch pad". (unlike SpaceX needing west and east coast pads)
You can move your launch range to better ensure range availability
Smaller benefit = being able to pick up payload from customer lowering transport costs/time for payload

Problems include developing expensive carrier vehicle (stratolaunch) but you could just use of the shelf vehicles for smaller rockets (VG) and having people near the rocket during fuelling and launch



Offline Tulse

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Would it be incorrect to say that an additional advantage (at least at sufficient launch altitudes) is lower max-Q, which might allow for a lighter vehicle, and greater freedom in design (such as potentially larger fairings than a similar-sized ground-launched vehicle)? 

Presumably, such advantage largely disappears if the vehicle is reusable and has to return through the entire atmosphere.

Online envy887

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Sorry for digging up an old thread but am i right in saying the main advantages of air launch are not efficiency gains but;
A Very mobile launch pad (it literally flies)
This allows matching of the target obit's ground track meaning no more waiting days/weeks for launch windows only hours
This also allows launching into any inclination with the same "launch pad". (unlike SpaceX needing west and east coast pads)
You can move your launch range to better ensure range availability
Smaller benefit = being able to pick up payload from customer lowering transport costs/time for payload

Problems include developing expensive carrier vehicle (stratolaunch) but you could just use of the shelf vehicles for smaller rockets (VG) and having people near the rocket during fuelling and launch

There is no evidence that a custom airlaunch platform like a giant balloon or Stratolaunch is any cheaper than a fixed ground launch pad, or even several pads. Land-based pads can also be mobile, like ICBM launchers or Vector's system.

And launch azimuths for this air-launch system are constrained by landing runway sites for the suborbital booster spaceplane, and by overflight concerns for the upper orbital stage. Can't land that thing on a barge or even a ship of any reasonable size.

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