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How simple can a manned craft be?

Posted by: Andy Hill - Mon Feb 18, 2008 10:39 pm
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How simple can a manned craft be? 
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Post How simple can a manned craft be?   Posted on: Mon Feb 18, 2008 10:39 pm
There's an article over on the space review that discusses the need for complexity in manned spacecraft and I was wondering just how simple can a craft be made.

http://www.thespacereview.com/article/1061/1

If simplicity leads to reliabilty then why do rockets become increasingly more complex? While I accept that there is a need for some critical systems to be backed up such safegaurds should not be sophisticated or rely on many data inputs from numerous sensors.

So getting back to my question what would it be possible to use for a small manned orbital craft with a crew of 4-6 people? As a predudice I would like to use a craft that could have a certain amount of cross range during landing and preferably land on an airstrip to make it easier to hit and pick a targeted area.

I would like to get near the "spam in a can" approach but not have a totally uncontrolled landing and this craft would not need to remain on orbit as an autonomous craft for more than about 12 hours (which should be long enough for a couple of attempts to dock with a space station and if still unsuccessful re-enter to a designated landing site). Ideas?

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Post    Posted on: Tue Feb 19, 2008 4:04 am
After reading that article I've got two things to say:
1. Threre are lie, damn lies and statistics
2. As comrade Stalin used to say perfection is enemy of good enough.

The statistics in that article are taken out of context and faulty logic is used to promote a design philosophy endemic to NASA and which arguably has been shown to be out of touch with reality. The logic used in the article is akin to argument "Drugs are good, therefore taking more drugs is better". I am not sure I'd even want to point out all the faults in that article there are so many of them, but I'll try.

First solid boosters are more reliable than liquid motors, provided they are machined to the same standart. Prime example of this is V series of rockets, everybody can make solid fuel rocket boosters with a bit of effort and yet it took quantum leaps in machining and engeneering just to get V rockets lift off rather than blow up on the launch pad. Most of solid fuel rocket failures are due to years of storage in missile siloes of the said rockets. I'd like to see a liquid fuel rocket do the same. That's why hybrid rockets are so exciting they combine the reliability and ease of storage of solid fuel rockets and performance and control of liquid fuel rockets.

Second, more complexity is better philosophy of NASA has been discredited everywhere but in NASA. The safest AND the cheapest space lauch system to the best of my knowledge is a humble Proton that failed only twice and flew more missions than shuttle with success rating close to 99%, while 2 out of five shuttles bit the dust despite the unprecedented safety expenditures.

Regarding orbiter as a plane sentiment. I think the majority would agree that reusable orbiter when you don't have reusable suborbital stages is an upside down way of doing things. Suborbital stages are far more expensive. Looking into economics of things, even most optimistic cost projection for advanced chemical propulsion tech puts the price to LEO at 100-1000$/kg and when you take into account that steel costs 1$/kg and spacegrade alloys in about $10/kg, disposable cheap tin can orbiter is far more attractive than reusable one with reduced playload. And ofcource expensive components like avionics can always be scavenged for later use.

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Post    Posted on: Tue Feb 19, 2008 7:35 am
Hello, Horus,

to your last point I can't agree that way. If the orbiter is reusable and if the suborbital stages are NOT reusable then this still is more economical than if even teh orbiter would be expendable.

Of course I don't like combinations of reusable orbiters with expendable stages. But the reason is that if the orbiter can be made reusable then the stages can be made reusable as well and easier perhaps - so it seems to be inconsequent and strange. It's missing or lacking economical advantages that could be got easyly. This would have to be justified by constraints - economical ones or skills or so.



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Post    Posted on: Tue Feb 19, 2008 1:59 pm
well, there are also other hidden cost associated with a manned space program other than the vehicle itself.

I don't see anyone mention testing. And I don't mean firing the engine. I notice most national space programs include a long testing regime ranging from systems integrations, radiation testing etc etc for months.


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Post    Posted on: Tue Feb 19, 2008 5:37 pm
I agree that it doesnt seem sensible to say that the more complexity you add to a craft, the more reliable it becomes, hence my original question.

If you make a hull out of light weight alloys and use relatively simple systems in it that dont require endless testing to validate I dont see why something cant be built fairly quickly without billions of dollars being flushed down the toilet.

For instance no need for solar panels, use a set of fuel cells for power.

For a reasonably small craft use a heatshield that can be replaced easily after every flight if its cheaper. What is the point in using something like shuttle tiles that have been designed to be flown a number of times but in reality have to be regularly replaced and require unbelievably time consuming test procedures. Use something that can be sprayed on and removed off with a wallpaper scraper.

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Post    Posted on: Tue Feb 19, 2008 7:01 pm
I don't think anybody would make the mistake of considering the Space Shuttle as an example of a simple space vehicle. Orion will be simple in comparison. Dragon will probably be simpler still. Was a Mercury or Vostok as simple as possible? Probably not, but close.


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Post    Posted on: Tue Feb 19, 2008 7:26 pm
Criticizing NASA or any other organization based on "complexity bad - simplicity good" is silly.

If simplicity is better, then we should all immediately disable the ABS, air bags and seat belts on our cars, to give us a "better" simpler system.

Good design addresses constraints and conditions to meet specifications. And complexity is a concern, but certainly not the greatest.

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Post    Posted on: Wed Feb 20, 2008 12:55 am
The point is not that simplicity is good and complexity is bad but that overcomplexity is bad. If your car was build to the same standart as space shuttle, you would get something like formula 1 racecar on steroids prototype- dosens of cameras, front and back radar, thousands of sensors of every shape, size and description on every mech/electric part and state of the art engine but NO setbelt, airbag or even crumble zone. Well at least you get the satisfaction of knowing that if you do crash, your last moments will be recorded by thousands of instruments aboard.

On reusable orbiter, with chemical rockets getting to suborbital the shuttle way costs thousands of $ per kg. Shuttle playload is what, 30t? Plus the orbiter it becomes 100t plus, that's like worse than 1/2 playload to mass ratio. If the shuttle were to be partially disposable you can get palyload to mass ration of 3 easy, meaning you can get more than twice the playload into orbit. It's not a great engeneering challenge to design a tincan reentry vehicle thats largely recyclable, the most expensive part of a tin can is the computers, engines and simular complex devices, you can scavenge them, but the hull itself is dirt cheap compared to the playload.

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Post    Posted on: Wed Feb 20, 2008 2:58 pm
Hi Horus,

So then we both agree that this statement was oversimplified?

"Second, more complexity is better philosophy of NASA has been discredited everywhere but in NASA"

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Post    Posted on: Wed Feb 20, 2008 6:11 pm
It's not necceserily complexity or overcomplexity that drives the cost of rockets or the space shuttle. Once the complexity is designed, the major cost is maintenance. Looking at the space shuttle, it takes half an army to maintain it. And personnel costs are the biggest issue in every environment. So if you would design something that's perhaps overcomplex from a certain perspective, but extremely cheap to maintain, that would be a good thing.

But what do you/we mean with overcomplexity? I know that it is non-needed complexity, but let's take the car for example. What do you do with a car? You drive from A to B (maybe also to C) and go back to A. Safely, off course. Is a motormanagement-system needed for this? No, not per say, but it saves you fuel. Do you need electric windows to that? No, you can easily do it the old way. Power steering? Unless you're steering a 1,5+ ton car and you don't have muscles, yes.

So it all depends on our definition of what a simple or complexe or overcomplex spacecraft is.


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Post    Posted on: Wed Feb 20, 2008 8:41 pm
I think one of the problems with complexity is the extra weight it adds. I have always thought it strange that orbital craft that are supposedly made from light weight alloys always seem to mass more than a couple of tons.

In an environment where every kg costs a fortune to send in to space, including 100s of metres of additional cable and many extra sensors seems utter stupidity.

Didn't Burt Rutan rip out a load of stuff in SS1 for the final flight to get to a higher altitude?

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Post    Posted on: Thu Feb 21, 2008 1:39 am
A triangular truss is more complex than a solid beam of the same strength, yet is also lighter. Simple explanations for complex issues are sometimes appropriate, but not always.

The appropriate question to ask about whether SS1 had a bunch of stuff ripped out before flight is either: Why did they put in all that stuff they didn't need? or What did they risk by removing that stuff?

No good engineer makes things more complicated for the hell of it. NASA and many other old.space and alt.space organizations have good engineers.

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Post    Posted on: Thu Feb 21, 2008 3:50 am
Andy Hill wrote:
Didn't Burt Rutan rip out a load of stuff in SS1 for the final flight to get to a higher altitude?
Nothing was removed. They just filled up the oxidizer tank all the way to get every last bit of engine performance. I heard Burt say at a speech he gave at the University of Texas at Austin that the white layer around the middle of SS1 on the last flight was insulation because the oxidizer tank was full with little or no ullage. And I remember that was the only flight to have that. Image


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Post    Posted on: Thu Feb 21, 2008 11:53 am
campbelp2002 wrote:
Andy Hill wrote:
Didn't Burt Rutan rip out a load of stuff in SS1 for the final flight to get to a higher altitude?
Nothing was removed. They just filled up the oxidizer tank all the way to get every last bit of engine performance. I heard Burt say at a speech he gave at the University of Texas at Austin that the white layer around the middle of SS1 on the last flight was insulation because the oxidizer tank was full with little or no ullage. And I remember that was the only flight to have that.


What you say about the oxidizer tank is probably correct but I was pretty certain that they also removed some wiring that reduced the weight by a couple of kgs to gain some extra height.

Anyway back on topic, I wasn't really talking about the complexity of the structure's trusses I was thinking more about the inclusion of numerous backup systems and the associated wiring/electronics/sensors that go with them. Or even simple things like using black/white LCD displays rather than full colour for pilot instrumentation, such a change would probably save weight (monochrome devices are normally lighter) and less wiring is required (single coax rather than an RGB input). Also much easier to maintain or trouble shoot. Applying this type of reasoning to a craft's systems should make it easier to produce.

One of the things I have found is a tendancy to move the goal posts of a project and keep including additional features to a system when they are not really needed and could be done without. This often leads to longer delivery times and additional cost, I am advocating paring such things down to a bare bones craft.

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Post    Posted on: Fri Feb 22, 2008 12:55 am
That is a well known and documented phenomenon in computer science, called feature creep, or featuritis when it's all-pervasive.

http://en.wikipedia.org/wiki/Functionality_creep
http://en.wikipedia.org/wiki/Featuritis


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