It really is a shame. When all you have is a hammer, everything else looks like a nail. This also applies to our current, international space programs.
We have been using chemical rockets for centuries, but since the advent of V2s and the modern space age, these brute-force and cheap work horses have been the main propulsion technology we use to go just about everywhere in the solar system. But this amounts to thinking that one technology can span all of our needs, and the trillions of cubic miles that encompass interplanetary space.
We pay a huge price for this belief.
Chemical rockets have their place in space travel. They are fantastic ways of delivering HUGE thrusts quickly; the method par excellance for getting us off this planet and paying the admission ticket to space. No other known propulsion technology is as cheap, simple, and technologically elegant as chemical propulsion in this setting. Applying this same technology to interplanetary travel beyond the moon is quite another thing, and sets in motion an escalating series of difficult problems.
Every interplanetary spacecraft launched so far to travel to each of the planets in our solar system works on the exact same principle. Give the spacecraft a HUGE boost to get it off the launch pad, and with enough velocity to reach the distant planet, then cut the engines off after a few minutes so the spacecraft can literally coast the whole way. With a few more ‘Delta-V’ changes, this is called the minimum –energy trajectory or for rocket scientists the Hohmann Transfer orbit. It is designed to get you there, not in the shortest time, but using the least amount of energy. In propulsion, energy is money. We use souped-up Atlas rockets at a few hundred million dollars a pop to launch space craft to the outer planets. We don’t use even larger and expensive Saturn V rockets that deliver even more energy for a dramatically-shorter ride.
If you bank on taking the slow-boat to Mars rather than a more energetic ride, this leads to all sorts of problems. The biggest of these is that the inexpensive 220-day journeys let humans build up all sorts of nasty medical problems that short 2-week trips would completely eliminate. In fact, the entire edifice of the $150 billion International Space Station is there to explore the extended human stays in space that are demanded by Hohmann Transfer orbits and chemical propulsion. We pay a costly price to keep using cheap chemical rockets that deliver long stays in space, and cause major problems that are expensive to patch-up afterwards. The entire investment in the ISS could have been eliminated if we focused on getting the travel times in space down to a few weeks.
You do not need Star Trek warp technology to do this!
Since the 1960s, NASA engineers and academic ‘think tanks’ have designed nuclear rocket engines and ion rocket engines, both show enormous promise in breaking the hegemony of chemical transportation. The NASA nuclear rocket program began in the e arly-1960s and built several operational prototypes, but the program was abandoned in the late 1960s because nuclear rockets were extremely messy, heavy, and had a nasty habit of slowly vaporizing the nuclear reactor and blowing it out the rocket engine! Yet, Wernher Von Braun designed a Mars expedition for the 1970s in which several, heavy 100-ton nuclear motors would be placed in orbit by a Saturn V and then incorporated into an set of three interplanetary transports. This program was canceled when the Apollo program was ended and there was no longer a conventional need for the massive Saturn V rockets. But ion rockets continued to be developed and today several of these have already been used on interplanetary spacecraft like Deep Space 1 and Dawn. The plans for humans on Mars in 2030s rely on ion rocket propulsion powered by massive solar panels.
Unlike chemical rockets, which limit spacecraft speeds to a few kilometers/sec, ion rockets can be developed with speeds up to several thousand km/sec. All that they need is more thrust, and to get that they need low-mass power plants in the gigawatt range. ‘Rocket scientists’ gauge engine designs based on their Specific Impulse, which is the exhaust speed divided by the acceleration of gravity on Earth. Chemical rockets can only provide SIs of 300 seconds, but ion engine designs can reach 30,000 seconds or more! With these engine designs, you can travel to Mars in SIX DAYS, and a jaunt to Pluto can take a neat 2 months! Under these conditions, most of the problems and hazards of prolonged human travel in space are eliminated.
But instead of putting our money into perfecting these engine designs, we keep building chemical rockets and investing billions of dollars trying to keep our long-term passengers alive.
Check back here on Friday, March 17 for a new blog!
One thought on “Hohmann’s Tyrany”
My figuring is the problem is to find a light-weight power source in the gigawatt range. My SF novels assume fusion power, but (a) we don’t have that, and (b) it wouldn’t be light-weight. It is not that easy to find such a desirable power source, unfortunately.
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