Control cost or go home

Impaler · 2012-06-14 16:57:57

Clark: Your SSTO link seems to completely neglect that SSTO is pointless if the vehicle is also Expendable, if it's going to fly once then maximizing payload by shedding dry mass on the way up is the optimum strategy no matter how high the efficiency of the engine. A vehicle must be reusable before SSTO even becomes a possibility economically, and even then a dis-assembly on assent and re-assembly on the ground still makes a lot of sense. A strait up SSTO rocket is going to have incredibly challenging re-entry that will cut into it's payload mass, that's why the Ventur-Star failed they just ran into a engineering brick-wall that could not be surmounted at any cost.

I'm also very skeptical of this rail-gun concept. While we can certainly fire projectiles at high speed their would need to be a significant amount of equipment in this 'shell' in-order for it to guide itself into the desired orbit and dock and probably some propellant too. A ground based gun can sustain a high launch rate, but can the receiving orbital facility that's catching these shells safely receive them that fast? Docking something to the ISS takes nearly a day for the necessary safe approach vectors and when you have to receive thousands of deliveries each one needs to be very safe or else the risk to the receiving facility will be unacceptably high. It doesn't seem to me that any of these Gun-launcher systems have put ANY though into the Earth orbit receiving end of the system. After all this is basically the work of weapon system developers who have been working for the Navy, weapon designers don't tend to not think much about the projectile once it leaves the end of the barrel.

SpaceNut · 2012-06-14 21:10:27

The problem witha rocket that is SSTO is that the large rocket must then have a heat shield to match, parachutes and I am sure that its going to be damaged by a water or land landing unless its a powered glider......

RGClark · 2012-06-15 01:31:02

Impaler wrote:

Clark: Your SSTO link seems to completely neglect that SSTO is pointless if the vehicle is also Expendable, if it's going to fly once then maximizing payload by shedding dry mass on the way up is the optimum strategy no matter how high the efficiency of the engine. A vehicle must be reusable before SSTO even becomes a possibility economically, and even then a dis-assembly on assent and re-assembly on the ground still makes a lot of sense.

Take a look at the very insightful quote of Arthur C. Clarke I put at the beginning of the blog post.

Bob Clark

Last edited by RGClark (2012-06-15 06:06:55)

Terraformer · 2012-06-15 04:22:17

I don't think the station is supposed to catch the payloads dirextly. I've always thought they'd use an orbital tug (using an Arcjet?) to catch the payloads and take them to the station, so that payloads can be launched dumb and have an upper stage already on orbit...

RGClark · 2012-06-15 07:13:51

RGClark wrote:

Good point about gas gun launch being doable now for small payloads. Do you have a link to this teams research?

I found the gun launch researchers by searching on the Mars Society conference for 2011:

Report on the 2011 Mars Society Annual Convention
posted Aug 16, 2011 10:36 AM by Michael Stoltz [ updated Aug 16, 2011 10:46 AM ]
By Richard Obousy, Centauri Dreams (centauri-dreams.org), 08.16.11

One talk that still resonates with me was given by Dr. John Hunter, an ex-theoretical physicist turned space engineer. Hunter is the director of Quicklaunch, a company planning to use a light gas gun to launch payloads into space. The basic idea behind the gas gun is to use a large piston which imparts force to a gaseous working fluid through a smaller diameter barrel which contains the projectile to be accelerated. The gun that Hunter is working on gives the projectile, a single stage rocket engine plus payload, an initial speed of 6 km/s which launches it to approximately 100 km altitude.
At this point, the rocket engine fires and gives the projectile the final kick it needs to circularize its orbit. Using this technique, Hunter believes that he will be able to attain launch costs of $500/lb. Contrast this with the Space Shuttle costs of around $10,000/lb and the economics quickly makes sense. Even Elon Musk’s heavy Falcon launcher will be around the $1000/lb mark, so Hunter’s gas gun looks like an attractive option! One obvious limitation is that the high gee forces (~100 g’s) experienced during the initial launch exclude the possibility of human passengers, and so the gas gun will likely focus on launching propellant payloads. The resulting fuel ‘depots’ could enable future manned lunar and Mars exploration, if Quicklaunch were used in tandem with traditional launch systems. I encourage anyone interested in this fascinating technology to take a look at the Quicklaunch website which contains more details on their plans and accomplishments to date.
https://sites.google.com/a/marssociety. … convention

Propellant Delivery to Orbit in Support of Mars Exploration with Hydrogen Gas Guns - Dr. John Hunter.
http://www.youtube.com/watch?v=s7RGSBOmsm4

Bob Clark

GW Johnson · 2012-06-16 17:10:45

John Hunter, that's the one I remember. His paper was right before mine, in the very same session.

It's an angled launch into a transfer ellipse. He was proposing a light gas gun floating in the ocean. At apogee, you need a kick motor to circularize. At 100+ gees, that kick motor is more likely a solid propellant motor than a liquid. I've worked on solid designs good to 20,000 gees. The trouble is, delivered impulse is less precise than one would like for the mission at hand, because it is fixed.

There must have been some sort of attitude thruster design on the old Sprint ABM, another 100+ gee system. A simple solid kick motor to rough-circularize, followed by detailed trim with that 100+ gee thruster design, could do the job we are talking about here.

Tanks tough enough to haul propellant up in a light gas gun launch, would likely be tough enough to survive re-entry with very minimal provisions. Now we are looking at a reusable propellant delivery tank! Imagine that.

GW

Rune · 2012-06-18 09:14:07

Solid rockets may be reused, but I think we could take a page from the SRB's and stop deluding ourselves that that is going to save any money.

Other than that, the gun is neat. Makes me think of a launch loop in small scale. Maybe by building things like these we will build confidence for the time when the magic material appears and we can build the elevator and be done with atmospheric rocketry.

Rune. "Reusing" a solid rocket engine in the real world means rebuilding it.

GW Johnson · 2012-06-18 09:52:42

Solids are cheap and easy enough not to reuse. Especially for a kick motor application. They've been used since the early 60's as kick motors.

GW

Mars_B4_Moon · Today 12:31:31

A new direction but NASA's SLS rocket 4-5 Billion?

NASA wants a cheaper Mars Sample Return—Boeing proposes most expensive rocket
https://arstechnica.com/space/2024/05/n … ve-rocket/

New Mars Forums

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#51 2012-06-14 16:57:57

Re: Control cost or go home

#52 2012-06-14 21:10:27

Re: Control cost or go home

#53 2012-06-15 01:31:02

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#54 2012-06-15 04:22:17

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#55 2012-06-15 07:13:51

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