guest blogger john hare
Ramjets come up just about every time someone takes a fresh look at space launch. It seems such an obvious approach that very few of us have skipped looking into them. The trade studies that have been done repeatedly show that there is no benefit to their use in acceleration missions, which space launch is. The problem is that an intelligent person taking a fresh look at the problem is usually unaware that most of us have looked, and that many of us have been in the same argument dozens of times over the years. I spent time and money (small amounts by industry standards) checking it out for myself. Something that looks that good is not something you drop because somebody you never met says so.
I thought I would draw one of my little cartoons to illustrate the way some of us see the problem. Sometimes a visual image to hang the discussion on helps get the point across in both directions. It is also possible that the new player will see something that everybody else has missed.
The rocket on the left is straightforward two stages to orbit with no frills. In the center is the turborocket that I play with which still requires two stages above the launch assist platform. On the right is the ramjet system with a rocket booster to get the vehicle up to ramjet speeds, then ramjet, then still two stages to reach orbit due to the mass penalty of the thermal protection during the ramjet phase. In the launch paths, the rocket is out of the thicker atmosphere by mach three, while the turborocket is there a little longer, while the ramjet has to stay in the air for minutes more with stagnation temperatures well over 1,000 degrees. In addition to the thermal protection, the ramjet vehicle must also have an airframe that provides lift and is controlableÂ from mach 2 through 6. Turning the first two stages into an ejector ramjet doesn’t substantially change the ratios.
The references I have found by experienced investigators that still advocate ramjets for launch are virtually all written by people with a financial interest in keeping the discussion open, read grants.
If you believe you see a way for the ramjets to improve space launch, by all means investigate them. You might be the one that finds a good path. While you are at it though, remember that we don’t take your arguments for any more seriously than you take our arguments against. We can have good productive discussions so long as the parties concerned are respectful of others positions and courteous in making their points. The productivity of the discussion goes away when winning the argument becomes more important than seeking the truth. It is somewhat more difficult in this case because it has been going on for so long.