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We have a large number of topics about launch systems over various kinds.
I looked at all of them and found none that seems a good match for this item ...
I'll put the opening article in Post #2
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https://techcrunch.com/2023/07/10/longs … cheap-too/
Space
Longshot Space wants to make space launch dumb — and really cheap
Aria Alamalhodaei@breadfrom / 1:04 PM EDT•July 10, 2023
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Image Credits: Getty Images
Rockets are among the greatest feats in human engineering, but to Longshot Space CEO Mike Grace, they’re an “overly exquisite solution” to the problem of sending megatons of inert mass to space.“You need something that is dumber and much cheaper, both to build and to operate,” he said in a recent interview.
Longshot’s answer is a kinetic launch system that will be capable of reaching hypersonic speeds and shooting projectiles to orbital velocities, for less than the cost of a Netflix subscription. It’s noticeably different than its competitors — specifically SpinLaunch, which is developing a spinning accelerator to shoot mass to orbit, and Stratolaunch, which uses a giant, specialized plane to release a hypersonic vehicle midair — in appearance and approach.
The biggest difference is that Longshot’s system is very, very horizontal. It is not technically a gun, as it doesn’t use an ignitor; instead, compressed gas squeezes a wedged projectile down a very long concrete tunnel that’s basically a vacuum chamber. The resultant speeds are extremely fast, and they increase in proportion to the size of the system.
That means a system capable of Mach 5 will be around 80 feet long; a Mach 10 system, the size of two or three football fields; and systems capable of getting to space, at Mach 25 to 30, on the order of multiple kilometers long.
It’s a staggering scale, but Longshot is aiming for a very lost cost to orbit — as low as $10 per kilogram to orbit (in comparison, the price tag of a Falcon 9 ride-share is $6,500 per kilogram). According to the company, its low prices are only achievable by keeping as much of the system on the ground as possible. Energy is stretched out over space and time; freed from the demands of vertical lift, such systems can suddenly be built out of concrete, rather than aluminum.
But there is no free lunch, especially in aerospace, and Longshot’s cheap prices will come with some major trade-offs. The first is the land footprint. Longshot’s system includes an on-site solar farm, in addition to the compressed gas pumps and tunnel, that will no doubt help keep costs low but add to the overall land-use requirements.
The other trade-off is noise. At such sizes, Longshot’s system will generate an extraordinary sonic boom. Given that the company will be able to reuse the system as quickly as it can draw a vacuum in the tunnel, that could mean many sonic booms per day. For these two reasons, the system will have to be sited somewhere very, very remote — think the Australian bush or the arid regions of Kenya.
“You would want to be somewhere where an atomic bomb could go off and nobody would notice,” Grace said.
These trade-offs could prove to be relatively trivial, should humanity finally consummate its desire to colonize the solar system. Grace pointed out that Hawaii imports 13 million tons of stuff, including food, gas to power cars, plastic products and more, for a population of around 1.4 million. An off-world colony — without the plentiful fresh water, atmosphere, soil, and everything else in our biosphere that aligns to make life possible — would need to import more. A lot more.
“Right now, that’s not really practical,” Grace said. “I don’t think it may ever be practical with rockets. So the question is, how do you drive the price of putting material in space through the floor?”
Elon Musk’s SpaceX is also looking to solve this problem, with its super-heavy Starship vehicle that will be capable of lifting upward of 250 metric tons to orbit in an expendable configuration. But Grace is not convinced that the economics of Starship will ever fully be able to compete with Longshot’s own system.
“I would expect [SpaceX] to spend somewhere between $5 [billion] and $30 billion on Starship before it’s good to go,” he said. “They’re going to need to get that money back. […] Some of Elon’s more hyperbolic comments about the price they’re going to be able to hit, maybe those are true, but it might be on a 40- or 50-year timescale. They might need to amortize those costs out for a very long time.”
That doesn’t mean Longshot would make Starship obsolete. The enormous amount of G pressure that would be generated by Longshot’s system is wholly unsuitable for the human body, so any person who wanted to go to space would be much better off on a rocket.
Longshot has gotten notably far with relatively little in funding. Since closing a $1.5 million pre-seed round last April, from investors that include Sam Altman, Draper VC and SpaceFund, and being awarded a direct-to-Phase II SBIR from the Air Force Research Laboratory, Longshot has built a test accelerator from its headquarters in Oakland, California, and achieved speeds up to Mach 2.2. Grace said he anticipates demonstrating speeds north of Mach 5 within a month.
Longshot’s demonstrator system. Image Credits: Longshot Space (opens in a new window)
In the short-term, Longshot wants to piggyback off the U.S. Department of Defense’s need for hypersonic capability, land some contracts, and use that revenue to essentially subsidize the development of a really big, really cheap launch system for space. On a longer time horizon, Grace said the real money will be made not from the launch system but by growing demand for services that Longshot offers in space.
“The key to being able to support that is having a system that can do it at extremely low cost,” he said. “You’ve got to get a system that is designed to be as dumb as hell.”
“Make it bigger. Don’t make it smarter. That’s expensive.”
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This reference examines the liquid nitrogen hot water rocket engine. I can only see the abstract.
https://ui.adsabs.harvard.edu/abs/2010J … W/abstract
I have often wondered about this option in support of a launch assist system. The idea is to boost a rocket to roughly Mach 1 velocity using a rocket sled. This would save a great deal of propellant, potentially allowing the rocket to function as an SSTO. The LN2-H2O rocket would have an exhaust velocity of ~500m/s. Sufficient for a Mach 1 staging velocity. The advantage of this rocket for launch assist are:
1) Hot water and LN2 are energy cheap propellants that can be produced using carbon free energy, even direct solar or nuclear heat and a mechanically powered liquefaction plant;
2) Both can be stored at low pressure (unlike the steam rocket). This reduces the dead weight of the sled;
3) The temperature of the system is low and the engine does not require cooling. There are no wall regression issues.
4) The sled can be refilled and used in rapid succession with no requirement for interlaunch maintenance.
5) The exhaust products are nitrogen gas and water ice particles, which are entirely non-polluting.
Accelerating to Mach 1 (343m/s) at 3g, would require a track length of 2km.
Last edited by Calliban (2023-10-02 06:04:26)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Calliban re #3
Thank you for this promising addition to the topic!
If anyone has an account to see the reference, please add to this topic.
Or, if anyone finds information about this initiative, not from the Harvard source, please add it here.
***
For the sake of completeness, I would like to point out that the launch system designed by Dr. John Hunter, and reported at length elsewhere in this forum, also would use compressed gas to launch a projectile. Dr. Hunter's design features hydrogen gas in order to reach near orbital speeds.
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Here is an open source paper on the nitrogen-water rocket.
https://www.jstage.jst.go.jp/article/ts … Ph_75/_pdf
Maximum ISP is 54 seconds, giving a maximum exhaust velocity of 530m/s. To achieve this, LN2 and hot water are sprayed into the expansion chamber at a ratio of 1:1.
Using the rocket equation and assuming a mass ratio of 2, gives a maximum achievable velicity of 367m/s. A mass ratio of two, would mean that the empty mass of the sled and the rocket payload mounted on it, would account for one half of launch mass.
Starship upper stage has a gross mass (fuelled) of 1300te and will carry 150te of payload.
https://en.m.wikipedia.org/wiki/SpaceX_Starship
If we assume the sled has an empty mass about the same, takeoff mass including the LN2 and H20, would be 5800 tonnes, of which 1450te would be N2 and another 1450te of hot water. It would be really neat if we could produce a heat pump that would generate both the liquid nitrogen and hot water with the same cycle. I wonder if that is possible?
To simplify the design of this rocket system, we would eliminate all pumps. The sled rocket would be pressure-fed, using compressed air in both tanks. The sled will be launched by opening valves of each tank. This woukd be actuated by the same compressed air system used for pressurisation.
Refilling of the sled with LN2 and hot water from storage tanks, will be gravity fed. Slowing the sled down at the end of the track after stage seperation, will be accomplished by momentum transfer into water, which will fill a gulley running down the centre of the track. The track will be mounted on an incline of about 45°. A water tank will be positioned at the end of the track. When the sled passes a set trigger point, a sluice on the tank opens and water drains by gravity into the gulley. The fully arrested sled then returns to its starting point at the bottom of the track by gravity. The starship would be mounted on a cradle. A low level transfer system would transport the cradle to the top of the sled. The ship will be held in place on the cradle by clamps, which are unlocked by a compressed air charge. Compressed air will be stored in high alloy steel tanks mounted on the sled.
Last edited by Calliban (2023-10-02 08:06:46)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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I'll open this post with another note of appreciation to Calliban for his substantial contributions to this topic! I am hoping he will continue researching the LN2 / hot water concept, and perhaps provide some links with images to show how the concept might be realized.
This post is another of a series on Dr. John Hunter's concept for a gas gun capable of launching substantial mass to a velocity sufficient to reach LEO, assuming part of the mass includes a solid fuel rocket for orbit circularization.
I am attempting to "reverse engineer" Dr. Hunter's Design, since most of the relevant details are proprietary (with good reason).
In addition, however, I am attempting to extend what I understand to be the basic idea, to see if it can launch a ton to escape velocity. For this purpose, I have enlisted ChatGPT(4). However, anyone using ChatGPT(4) is advised to double and triple check the figures it produces.
With that caveat in mind, I will post preliminary results from a recent inquiry. I fully expect there are errors in play, but I cannot see them. By posting the results, i am hoping to enlist the insight/wisdom of forum members to point them out.
The specific value about which I am skeptical is the estimate of 184 bar for the pressure on the base of a projectile that is leaving the exit port of a 1 kilometer long tube at 11 km/s. ChatGPT(4) seems to think the pressure at that point is sufficient, but I found with a quick search that the pressure inside a 155 mm artillery barrel can reach 3000 bar. That pressure may be required due to the short length of the barrel, but never-the-less, it makes me skeptical that the 184 bar figure ChatGPT(4) came up with is correct.
opening specifications for calculation
Parameters:
Diameter of tube: 2 meters
Exit velocity: 11,000 m/s
Mass of payload: 1,000 kg
Length of tube: 1,000 meters
Propellant gas: Hydrogen
Conclusion:
Summary:Time required for acceleration: Approximately
0.19 secondsAcceleration required: Approximately 57,895 m/s2
Pressure at exit: Approximately 184.39 bars
If there is a member willing to check those numbers independently I'd appreciate the assistance.
I think the acceleration and time are likely to be close to right, because they can be derived by using well known equations.
The question I have is the pressure figure. That figure might be right, but the figure of 3000 bar for the interior of a 155 mm artillery barrel makes me skeptical that the 184 bar figure is right.
It may be right, but I sure would appreciate confirmation, or correction.
The actual (correct) pressure is needed to size the launch tube correctly.
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