5 Responses

1. Yech! No need to shout.

   That’s up to whom ever wants to invest in the project.

2. Anytime a question starts with “Why can (can’t?) we have more funds for…”

   …it’s not a scientific question, it’s a social, political and financial one.

   If Dr Diaz’ invention has technical merit, satisfies a technical need, and impresses enough people who hold the purse strings, then it will get funding.

   Otherwise, it’s back in line….

3. BECAUSE USING ALL CAPITAL LETTER IS RUDE, AND NO ONE WOULD GIVE MONEY TO THOSE WHO USE ALL CAPITAL LETTERS.

4. VASIMR should be cancelled. Don’t get me wrong I am a strong proponent of manned space exploration but I am in favour of doing it the right way. Brass tacks engineering, not over bloated science projects that cost 100 times what they need to.
   The problem is VASIMR is that it cannot do the things it claims it can do. For example Diaz claims it can get you to Mars in 39 days. They engine cannot do that. It’ll get you to Mars in 6 months like any other rocket. VASIMR (I’m just going to call it VR from now on for short) might have advantages if you were doing a mission to say Saturn, because it would cut down launch mass. But if you wanted a Lunar or Mars mission, it’s more trouble than it’s worth and in order to sell it to NASA they are making assumptions that are completely unfounded.
   First of all, VR needs about a 2 megawatt reactor before it really hits it’s sweet spot. That is 30 times the size of the biggest reactor ever put in space (which is the one on the ISS which is about 75 kilowatts) so right away you’ve got a problem, because you’ve got a propulsion system with an energy source that doesn’t exist.
   Second, Diaz assumes an alpha of one (alpha is his unit of power to weight ratio). Travel time is directly proportional to thrust, thrust is proportional to power and the power is proportional to the mass of the reactor (and that includes all that goes with the reactor which in reality makes up most of the mass). So if I say this has an alpha of 100, then that means you will get 1 kilowatt per 100kilograms. You get the general idea.
   An alpha of 100 is about what most flight ready reactors can do. There are some projects which aim to get this down to about 65. Realistic I would say. It might be possible (and when I say possible I mean several radical leaps in the current state of the art) to talk about an alpha of 20-25.
   Diaz assumes an alpha of one. That is impossible. This is 2 orders of magnitude better than the real world. Imagine something strong as titanium, but lighter than a styrofoam cup.
   If we could fabricate materials with those properties, never mind single-stage-to-orbit, we could just do single stage to Mars. It would be easy, you wouldn’t need VR, you wouldn’t need anything.
   Let’s assume an alpha of 20, which is an engineer’s wildest fantasy. With 20kg per kilowatt, that means a 2 megawatt VR engine weighs about 4,000 tonnes.
   This would need to be build in orbit with about 100 consecutive launches. And this is 4,000 tonnes of extremely expensive technology, not cheap rocket fuel. It becomes a logistical nightmare. And all this to push a craft to Mars which weighs 40 tonnes, and still takes 180 days.
   If you want to do a Lunar or Mars mission you do it Apollo style. Heavy lift booster on a direct throw from Earth, you get to the moon in 4 days and Mars in about 6 months.

5. Based on what I’ve read, the technology is not suitable for lunar launches, except perhaps slow cargo runs. A vasimr rocket can not take off from the surface of the Earth or even the Moon. It is strictly a deep space engine.