“Work is about to start” on “fusion rockets”…when we could have spaceships, true spaceships, exploring that first icy body in our system closest to Earth (Ceres) in a relatively short Apollo-program time frame. A “Medusa” spaceship could be lofted into polar orbit in 100 ton modules that would dock with each other and in the right orbit could possibly light off their “pulse units” (bombs) without any or a very small amount of byproducts entering Earth’s magnetosphere. If each H-bomb can impart 100 mph then 1000 bombs can provide 100,000 mph. Using this figure for travels to icy bodies in the outer system a rough one way travel time can be estimated. I did some very rough guesses of travel times several years ago in the blog entry titled “Interplanetary Missions.” One thousand bombs might provoke automatic naysaying but a Trident missile can carry 14 warheads and an Ohio class submarine can carry 24 missiles with 336 warheads on board. Since the “bus” that carries the warhead is only the nose section of a missile, a dozen or more carousel type platforms (a ten warhead Peacekeeper missile carousel is shown below) could all be stacked in just one of the four launch tubes shown. The four launch tube construct shown could carry over 400 warheads in stacked carousels as described and gives a good idea of the scale needed for pulse unit storage on interplanetary missions.
1000 bombs will get you out there but to stop anywhere requires another thousand. To come back to Earth requires another couple thousand to accelerate and then slow down again totaling approximately four thousand bombs, though this number can be lowered using different techniques. For missions to the gas or ice giants using gravity assist and the atmospheres of these bodies to slow down it might be possible to decrease the number of bombs to around 2000 and still maintain a high speed/low transit time. The “slugs” used to generate the cloud of plasma the bombs use to push the spaceship could also be derived from icy bodies and this would save mass. The cosmic ray water shield could also be utilized as a source for slug mass and this would restrict the crew space or likely dose the crew for a short period till the shield could be replaced with the water derived from the destination icy body.
The key feature of Nuclear Pulse Propulsion is the larger the plate (in a “hard” system like Orion) or spinnaker (in a “soft” system like Medusa) the more efficient the pulse units become. Extremely large spaceships on a scale we are simply not used to thinking about are far more efficient. It is akin to comparing airliners and container ships with the container ships going fast and the airliners slow. Until we have an industrial infrastructure on the Moon that can manufacture plates close to a thousand feet across we will be wasting fissile material. However the waste would be justified for initial exploration missions and future fissile material stocks could be replenished with lunar thorium-transuranics or breeder reactors.
Launch points for a nuclear pulse mission must be outside of Earth’s magnetosphere- either cislunar or possibly a super-eccentric Earth polar orbit.
1. Moon 2.380 km/s =4.70 times less escape velocity than Earth
Material can be lifted from the Moon into space using 23 to 25 times less energy than from Earth. For every hundred pounds sent into space from Earth over a ton can be lofted from the Moon. Since a true spaceship will require well over a thousand tons of water shielding for a small crew, the ice on the Moon is the place to acquire that shielding derived from lunar ice. Eventually the massive engine plates needed for super-efficient pulse drives will be manufactured on the Moon.
2. Ceres 0.510 km/s approximate travel time 140 days/4.6 months
Jupiter system 235 days/7.7 months
3. Ganymede 2.741 km/s
4. Europa 2.025 km/s
5. Callisto 2.440 km/s (outside of Jupiter’s radiation belts)
Saturnian system 424 days/14 months (1 year 2 months)
6. Mimas 0.159 km/s
7. Iapetus 0.573 km/s
8. Titan 2.639 km/s
9. Rhea 0.635 km/s
10.Dione 0.510 km/s
11.Tethys 0.394 km/s
12.Enceladus 0.239 km/s
Uranian system 777 days/26 months (2 years 2 months)
13.Miranda 0.193 km/s
14.Ariel 0.558 km/s
15.Umbriel 0.520 km/s
16.Titania 0.773 km/s
17.Oberon 0.726 km/s
Neptunian system 1190 days/40 months (3 years 4 months)
18.Triton 1.455 km/s (around a 7 year mission to visit my favorite moon round-trip)
Pluto is presently relatively close to Neptune’s orbit but is moving away from us and may be up to 5 billion miles away or farther before any mission is underway:
297 weeks/70 months (5 years 8 months)
19.Pluto 1.229 km/s
20.Charon 0.580 km/s
Most of my past comments on “The Space Review”, did not make it past the moderator, and I was recently banned for my criticism of NewSpace. Here are my edited original and follow-on comments:
I would speculate 100,000 miles per hour is the target speed for a unshielded spacecraft to take people to Mars. That would expose them to dosing and debilitation for only a couple months there and a couple months on the way back. The energy required to get the craft going that fast, then slowing down, then speeding back up, and finally slowing down minus a practical reentry speed, can be calculated and then evaluated using an Isp number. To go that fast is going to require nuclear energy as chemicals are almost useless. Nuclear Thermal Rockets only have an Isp about twice that of chemicals. That only leaves one practical propulsion system available right now with the least amount of development needed…and it is the one that seems to be verboten to even mention. I would add my firm belief that Mars, like LEO, is a dead end, and unshielded spacecraft are also a non-starter except for very short missions, such as intercepting Lunar Cyclers.
It is a binary problem of dosing AND debilitation. Concerning dosing I consider the basic popular science guide to be Eugene Parkers article in Scientific American, “Shielding Space Travelers.” Concerning debilitation I believe Gerard K. O’Neill’s classic book, “The High Frontier”, makes clear that Mars is not the place to go to live simply because humans evolved in one gravity. Just as our DNA will not tolerate cosmic radiation levels much beyond those found on Earth I also believe we will not thrive in lower gravities. Even if much lower gravity does not seriously debilitate, like microgravity, growing up in lower gravity will likely mean never being able to visit Earth.
The best path is to provide a Near Sea Level Radiation 1 Gravity environment (NSLR1G). This all falls in line when considering the massive shielding required, a tether-generated artificial gravity (TGAG) system being the only practical solution, and some form of nuclear propulsion being the only way to push such multi-thousand ton true spaceships around the solar system.