# Cheapest rocket to go to space?

Have you ever heard of the old movie Salvage? The TV movie, “Salvage,” aired on January 20, 1979. The film begins with Harry successfully bidding for a vintage bi-plane and then reselling it in pieces for more than twice that he paid for it. He’s using every penny he has to purchase up surplus military components, specifically, aerospace surplus, such as 3 XLR81-BA-7 (Agena) engines.

In short, he basically built a small rocket, went to the moon, and salvaged "it" without any professional help, using extremely powerful fuel.

I'm wondering if this could possibly be put into action, but not with strong fuel, just cheap stuff. I was thinking, maybe they should use liquid methane or liquid hydrogen, and even caught myself thinking of a liquid hydrogen, oxygen, and alcohol + carbon powder hybrid.

So, is a LH, LOX, and alcohol hybrid engine the cheapest means of space travel?

• I'm pretty sure this exact question has been asked here recently but I can't find it. – DarkDust Feb 23 '19 at 13:02
• @DarkDust: Here it is. It stalled at 4 reopen votes and was self-deleted. – Nathan Tuggy Feb 23 '19 at 19:08
• Should probably be worthy of note, if you're considering doing this-- don't. LH and LOX are extremely volatile and should not be handled outside of a controlled environment. Of least concern it's against the rules of the SE ;). – Magic Octopus Urn Feb 26 '19 at 19:27
• @Magic Octopus Um, DARN – AndrewMaxwellRockets Feb 26 '19 at 20:49
• @AndrewMaxwellRockets Hey man, things like that have been asked before :P – Magic Octopus Urn Feb 26 '19 at 21:16

They say space is hard. If you simply plop a big tube full of fuel and oxidizer on top of a surplus engine and light it, you will not go to space today.

To get a feel of the smallest shoestring you can have and still get to space, look at Rocket Lab in New Zealand. They've spent the last 10 years or so developing the ability to reliably go to space. Their Electron rocket is one of the smallest orbital rockets ever designed. It can send about 150 kg into orbit for the low, low price of $6 million. At \$40,000/kg that's quite expensive; SpaceX can lift much more at prices below \\$10,000/kg. What Electron offers is fast turn around time, a unique launch location (New Zealand), and a low total launch cost. And, I'm surprised to discover, it can reach the Moon! It's set to launch the 300 kg Moon Express in 2019.

Scott Manley has a nice video on the Electron. If you want to get a good feel for how hard it is to get into space, I highly recommend watching his other videos on rocket science.

But while 300 kg is enough to launch a few people, it isn't enough for all their stuff: food, water, oxygen, life support, suits, lander, ship to get home. And you can't simply scale up. Here's why.

A successful rocket requires solving a number of very, very hard problems in extreme conditions. Guidance systems, fuel pumps, nozzle designs, leaking fuel, cryogenics (liquid oxygen and hydrogen must be kept frozen), heat shields (you want to come back), staging, and so on.

Then getting into orbit requires not just going up 100 km, that's the easy part. It also requires going sideways at 8 km/s or about 29,000 km/h. This requires a delta-v of about 10km/s. Getting into lunar orbit requires an additional 6 km/s. And landing another 1.5 km/s.

Delta-v is, very roughly, a measure of how powerful your engine is and how long it can burn proportional to the mass of the vehicle. As mass goes up, delta-v drops. As mass goes down, delta-v increases. Due to the tyranny of the rocket equation, this is not a linear relationship. For every kg of mass you add, you have to add more fuel, which means more mass, which means more fuel. To get to low Earth orbit requires about 85% of the craft to be fuel. Staging is more efficient, but adds complications. Getting to the Moon requires an even worse fuel-fraction.

This is why getting three people, and 5,000 kg of their stuff, to the Moon was such a colossal undertaking. It wasn't just that we had to learn how to do it, it was because the scale was so enormous and expensive. It's why we haven't gone back. And it's why you can't make a rocket out of surplus parts and fly to the Moon.

• Not to even mention all of the supporting technologies. It's not just the rocket that was developed, but life support systems, launch platforms, DSN networks, fueling systems, etc... – Magic Octopus Urn Feb 26 '19 at 19:30
• "To get to low Earth orbit requires about 85% of the craft to be fuel. Staging is more efficient, but adds complications." Well, that's with staging. Even then, 85% is pretty generous. 90-92% is more common. – Nathan Tuggy Mar 18 '19 at 6:38

Salvage 1 was a TV series launched by a pilot TV movie (Salvage) in 1979. I watched the show during its original broadcast, enjoying the escapist fun, but quite cognizant that it was pure fantasy.

# Premise of the show

Harry Broderick (Andy Griffith) is a man running a salvage business who has a talent for economically exploiting what others might see as junk. He sees an opportunity in recovering hardware NASA left on the Moon during the Apollo program, and recruits a fuel expert and a former astronaut to help him build a rocket ship to retrieve it.

The fuel expert has a "magic" formula for something many times more powerful than has been used in any rocket. IIRC, in-show it was dismissed by NASA as too unstable.

The former astronaut has a pet theory for a sort of shortcut route to the Moon which NASA dismissed as "crank" science.

The combination of the magic fuel and shortcut route make feasible a rocket built on a shoestring budget that can execute a salvage of things NASA left behind on the Moon.

# Rocket Fuel

The Salvage 1 rocket fuel is pure Hollywood fiction. The John D. Clark book "Ignition!" presents an account of humanity's quest for the "best" possible rocket fuel ("best" depends on the qualities chosen to be of highest priority). The book lays out the numerous avenues of research and development and the corresponding outcomes. Based on the wisdom revealed in this book, no such fuel as depicted in the show could exist. There are limits to the amount/density of energy which can be stored chemically. The fuels which approach those theoretical limits are extremely difficult to handle - highly toxic (reactants and reaction products) and corrosive and/or unstable - basically expensive and dangerous to make and handle. Safer fuels (as commonly used) have less performance, but the difference is not "order of magnitude" as suggested by the show. A "super" fuel as depicted in the show simply could not exist, and anything approaching it could not be produced or handled on a shoestring budget.

# Shortcut to the Moon

The "shortcut" to the Moon demonstrates a lack of understanding by the show's writing staff of high school-level physics. The premise in the show is that going into orbit first is a costly and unnecessary exercise which can be avoided by taking a straight-line path. From a common-sense perspective, you might think this is true. However, the laws of physics show that the lowest cost approach is (more-or-less) to loft yourself above the atmosphere (well, most of it), then accelerate to orbital velocity so you don't fall back to Earth, and finally accelerate some more to get onto a transfer trajectory toward your destination. In actuality, these steps are somewhat blended together, but the key point is that, for an energy-efficient rocket-propelled flight, you can't get away from a mad dash to at least orbital velocity at some phase in the flight.

# Summary

The show threw in a few tidbits of "real science", but for the most part, sidestepped real physics and all sorts of problems which have to be solved to put a payload into space and deal with the space environment (zero gravity, no atmosphere, solar/cosmic radiation). This applies to both people and equipment. The show also distorted scale in all sorts of things, including the distance to the Moon and time required to traverse it, height of the atmosphere and (again) time required to safely travel between Earth's surface and a space environment.

The Apollo program was expensive, but it sought the "cheapest" possible route to the Moon in that the trajectory required the least (or thereabouts) amount of propellant possible at each phase. It also selected the most optimal propellant for each task.

• Getting what turned out to be a truly massive rocket off the ground took an enormous amount of thrust; RP-1 (refined kerosene) and liquid oxygen turn out to be the best choice in this role for a chemical rocket (as used in the Saturn V first stage).
• Getting up to orbital/transfer trajectory speed calls for high specific impulse - for a chemical rocket, this means liquid hydrogen and liquid oxygen (the Saturn V second and third stages).
• After a few days in space (the coast to lunar orbit), storability becomes a significant consideration, and because the crew is now beyond practical rescue, reliability is also a major concern, so hypergolic propellants are used, despite the lower specific impulse (Apollo CSM and LM).

What made Apollo expensive was partly that space is hard, and partly that the Kennedy mandate to go to the Moon had an aggressive timeframe attached to it. SpaceX is showing that access to space can be done less expensively, but you can only take things so far.

Just a few of the things that make rocketry and space travel expensive:

• Weight is critical, and everything adds up. Parts and materials need to be kept light while still being strong enough to do the required job.
• There is little or no room for defects. Shaving off weight means you leave little room for materials to be below spec. - everything has to be of high quality lest something important break and ruin your day. And generally, since you have to keep weight down, you only have what you need, so nothing is unimportant.
• Materials used in engine parts - combustion chambers, fuel pump turbine blades, and such have to withstand high temperatures and stresses simultaneously, and have to be made to fine tolerances. The materials and manufacturing processes to achieve that don't come cheap.
• Systems have to work in zero gravity. Dealing with the way fluids move in the absence of gravity can be a real trick.
• Systems have to work in a vacuum. In the absence of air, moving parts can vacuum weld together. Bearings etc. have to be designed and manufactured to work in a vacuum.
• You have to bring everything you're going to need with you. That can make for a long list, large quantities of supplies like air and water, and run up the mass budget.

Yes, you can make a cheap rocket, but a cheap rocket won't get you to space. To get to "cheap" you have to sacrifice important things. It may be too fragile and break; it may be too heavy and not take you very far; it may not carry enough propellant and again not take you very far; it may be too inefficient (low ISP) and not get you going fast enough; things may not work when needed because they weren't properly designed or tested for the environment they are in when called upon.

• Although I agree with you, I'm not saying to do it exactly as it was done in the movie, but rather if it is possible, even if it requires professional help, to create an extremely cheap rocket, but in such a way that it uses common materials(cornstarch starlight, fiberglass insl, cement tank first layer, etc...). – AndrewMaxwellRockets Feb 25 '19 at 12:33
• @AndrewMaxwellRockets "extremely cheap" is relative - SpaceX could be considered "extremely cheap", depending on your point of view. Nevertheless, one has to understand the scope and scale of the challenge in the real world. The cheaply built vehicle depicted in the show only worked because reality was bent sufficiently to permit it. Real rockets and rocket parts have to be built strong, light, defect free, and in the case of certain engine parts and heat shields - able to withstand very high temperatures. It's all these requirements that make things inevitably expensive. – Anthony X Feb 26 '19 at 1:59
• I'm saying, cheaper than any other life supporting spaceship ever created before. I think the cheapest one that made it to space was Electron, 6m(I don't know if people were on it). Therefore, would it be possible to use some hybrid, strong, cheap steel, homemade starlight, liquid hydrogen and/or methane a/o solid propellant(etc...) for first stage, and then LOX, alcarbon(alc+carbon), and LHY for second stage? And would it be practical? – AndrewMaxwellRockets Feb 26 '19 at 12:25
• @AndrewMaxwellRockets The simple answer is no. I mentioned Electron in my answer, one of the smallest rockets; though small doesn't mean simple. That took 10 years and 200 people and the first one blew up. The Electron's attraction is the low total price, unique launch location (New Zealand), and fast turn around time. But its payload is very small, far too small for a manned mission. Though it can reach the Moon, it's sending the 300kg Moon Express. – Schwern Feb 27 '19 at 0:29
• @everyone, Oh. okay. – AndrewMaxwellRockets Feb 27 '19 at 1:06