Author Topic: Stratospheric-Airship-Assisted Orbital Payload Launching System  (Read 2625 times)

Offline IRobot

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This starts to sound like the 25km high pyramid thread from 2 years ago...
Minimum advantage for a lot of trouble. Keep it simple!

Offline saaopl

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I actually shared Musk's view towards conventional air-launch approaches. In the AQ section of the following page, brief comments on two conventional air launch by plane and by balloon approaches have already been included.
http://saaopl.net/index.php/features/

One major reason that two conventional air launch are not promising, and yet to be mentioned by Musk, is that none of them are reusable, or neither of them can be an ideal candidate to develop a reusable launch system.

Actually, if you'll read the quote above from Musk it doesn't mention reusability at all.  Musk's point is valid even if you have full reusability.

Musk's point is that an aircraft-launched system essentially makes the aircraft an additional stage.  You have all the cost and complexity of an additional stage, but it's an additional stage that gives you much less benefit than a rocket stage.  The same is true for an airship-assisted launch system -- the airship is an additional stage, but one that gives you much less benefit than a rocket first stage.

You didn't address this point in your reply.


The cost and complexity of designing and constructing an airplane and an airship are at different level. The launch platform used in SAAOPL system can be much simpler than a conventional HAA at the same level. Structurally, it is a mix of an airship and balloon, with the maximum speed close to 40m/s at approximate 22km altitude, which is substantially lower than the maximum airplane speed of 200+ m/s at 10km. This difference alone already can save a lot of aerodynamic complexities.

Another thing to be emphasized that SAAOPL is an unconventional launching system. It is not a wisdom choice to isolate each components in the system and compare with conventional stages individually, rather than comparing systems as a whole. Taking the launch platform for example, if simply comparing it with conventional first stage in the scenario of launching an conventional upper stage, it doesn't worth at all, since it adds zero delta-V, lifts very limited altitude and doesn't boost reliability.  However, within SAAOPL system, the launch platform brings SLSS out of dense part of atmosphere (significantly boost the performance of SLSS), and provide the crucial altitude redundancy that SLSS needs to dump its fuel in the scenario of immediately-after-launch engine failure.

As a novel system, delivering a cargo to space orbit using SAAOPL system conceptually can be like sending a cargo to another continent using Boeing 747. The design of SAAOPL system have placed reusability, reliability and short-launch cycle in the key positions since the beginning.
« Last Edit: 04/18/2017 01:31 AM by saaopl »
Earth is the cradle of humanity, but one cannot live in a cradle forever  -- Konstantin Tsiolkovsky

Offline ChrisWilson68

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I actually shared Musk's view towards conventional air-launch approaches. In the AQ section of the following page, brief comments on two conventional air launch by plane and by balloon approaches have already been included.
http://saaopl.net/index.php/features/

One major reason that two conventional air launch are not promising, and yet to be mentioned by Musk, is that none of them are reusable, or neither of them can be an ideal candidate to develop a reusable launch system.

Actually, if you'll read the quote above from Musk it doesn't mention reusability at all.  Musk's point is valid even if you have full reusability.

Musk's point is that an aircraft-launched system essentially makes the aircraft an additional stage.  You have all the cost and complexity of an additional stage, but it's an additional stage that gives you much less benefit than a rocket stage.  The same is true for an airship-assisted launch system -- the airship is an additional stage, but one that gives you much less benefit than a rocket first stage.

You didn't address this point in your reply.

The cost and complexity of designing and constructing an airplane and an airship are at different level.

Your airship will need to be quite large, and development of that large airship will be expensive, as will operating it.

The launch platform used in SAAOPL system can be much simpler than a conventional HAA at the same level. Structurally, it is a mix of an airship and balloon, with the maximum speed close to 40m/s at approximate 22km altitude, which is substantially lower than the maximum airplane speed of 200+ m/s at 10km. This difference alone already can save a lot of aerodynamic complexities.

But it introduces other complexities, including a much larger structure and the need to maintain a very large, very lightweight structure.

Another thing to be emphasized that SAAOPL is an unconventional launching system. It is not a wisdom choice to isolate each components in the system and compare with conventional stages individually, rather than comparing systems as a whole.

If you take your SAAOPL system and replace the airship with a conventional rocket stage that is reusable, the system will become much better.  That is a valid criticism of the SAAOPL system.

Taking the launch platform for example, if simply comparing it with conventional first stage in the scenario of launching an conventional upper stage, it doesn't worth at all, since it adds zero delta-V, lifts very limited altitude and doesn't boost reliability.  However, within SAAOPL system, the launch platform brings SLSS out of dense part of atmosphere (significantly boost the performance of SLSS),

So does a conventional rocket first stage.

and provide the crucial altitude redundancy that SLSS needs to dump its fuel in the scenario of immediately-after-launch engine failure.

Many launch systems today have upper stages that cannot abort if the upper stage has a failure after stage separation.  And yet that very rarely causes a problem.  So your SAAOPL system is addressing a potential problem that really isn't important.

As a novel system, delivering a cargo to space orbit using SAAOPL system conceptually can be like sending a cargo to another continent using Boeing 747.

No.  You've provided no reason to consider launching to orbit using an airship as the first stage any more like using a 747 than launching using a Falcon 9.

The design of SAAOPL system have placed reusability, reliability and short-launch cycle in the key positions since the beginning.

So has Falcon 9 and so has Blue Origin's New Glenn.

Placing reusability or any other factor as a goal is meaningless if you make a bad architectural choice, and using an airship as a first stage is a really terrible architectural choice.

Offline saaopl

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The cost and complexity of designing and constructing an airplane and an airship are at different level.......



Let's summarize your key points first (Correct me if missed your points):
1 The lauch platform in SAAOPL system is too large. Hence, it should be complex and expensive to build, and hard to maintain.
2 The airship-based launch platform is a worse choice than a conventional rocket first stage even in SAAOPL system.
3 Upper stage rarely failed in previous launch missions. So, it is not worth to consider recovering SLSS.


Feedback:
1 The lauch platform in SAAOPL system is too large. Hence, it should be complex and expensive to build, and hard to maintain.

In a sample implementation that used to investigate and validate the concept of SAAOPL system, yes, the launch platform would be the largest aircraft in history if it is fully expanded at 22.3km altitude. This has been mentioned in previous posts. However, that doesn't mean it is a conceptually complex system, especially comparing with airplane or conventional high-altitude airship.

The largest component of the platform, hydrogen ballonet, is just a pressured streamlined balloon. Given the strength of envelope material is enough, any size of balloon would be possible to be built in a straightforward way: prepare balloon envelope, inflate lifting gas, and that is it.

Regarding to maintenance issue, as mentioned previously, the launch platform is highly lifting-gas-leaking tolerant. Its envelope mostly comprises of structural material, like Zylon, which also can be used for body armor. The conceptual upper limit of single SAAOPL system is approximate 1000-launches/year, which means 4 months continuous usage. As far as I know, material fatigue won't be a serious issue for Zylon if the loading is designed carefully, even taking into account the harsh environment in stratosphere.


2 The airship-based launch platform is a worse choice than a conventional rocket first stage even in SAAOPL system.

The launch platform is designed dedicatedly for SAAOPL. It is able to bring winged-SLSS out of dense portion of atmosphere at a very low speed (Less than 10m/s). If replace it with a conventional first stage that is already supersonic in dense atmosphere (more than 400m/s), how much aerodynamic complexity, dry mass penalty and risk would be added to SLSS and entire SAAOPL system?

Moreover, single SAAOPL system by design has a conceptual launch-frequency upper limit of 1000-launches/year. In such a high-frequency launch schedule, is there any conventional first stage, at least conceptually, can be reused without high risk to failure, without heavy maintenance workload, or even in a failure, the whole system can be survived and the payload can be recovered?


3 Upper stage rarely failed in previous launch missions. So, it is not worth to consider recovering SLSS.

This is simply not true. You might forget the loss of CRS-7 mission not long ago. This is already in a launch frequency much less than the conceptual goal of SAAOPL system. In many cases, the payload is more valuable than launch vehicle itself. In some special cases, so is the launch window.  For example, in Voyager program, if upper stage failed, that lost not only the space probe, but also the launch window once every 175 years. 

In SAAOPL's design, an engine failure of SLSS or other related issues probably just means another launch trial for the recovered payload within 8 hours, using a backup SLSS.
« Last Edit: 04/25/2017 12:03 PM by saaopl »
Earth is the cradle of humanity, but one cannot live in a cradle forever  -- Konstantin Tsiolkovsky

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