A Talk about Rockets

1956 May, KNN TV Studio

Welcome back to “The Design Hour” with guest visitor Gene Kerman, yes, your heard right, the very Gene Kerman leading our effort in reaching into the depths of space. So welcome Gene, first off, I heard there where some debate about who would join us today?

Gene: “Thanks, its nice to be here, and I look forward to telling the public a little about how things are working at the ISP. Yes, there where some talks, and eventually I, Bill, Bob and Wernher had a draw, and here I am.” Besides Bill and Wernher where pretty busy on our current rocket project.

Interviewer: “Sounds interesting, lets talk about that. What is the goal, and what are the interesting design issues.”

Gene: “Now that the interplanetary missions are done, for better or worse, we have started concentrating on returning to the Moon. At first we designed the Dove series of landing probes… ”

Interviewer: “Dove? Why doves?”

Gene: “Ah, well, that is because that is how we want to probe to land… like a dove. Seen especially in comparison with the previous landing witch was rather hard.”

Gene: “Anyways, our current rocket project is to develop a launch system able to place 10 tons of cargo in lunar orbit.”

Interviewer: “I note that the ISP already has the capacity to place 10 tons in LEO, how much more difficult is it to do the same at the Moon?”

Gene: “Its actually a lot worse. Lunar missions, are easy 3-4 times heavier, than similar LEO missions, and with added weight comes a lot of additional problems. Fortunately, our design skills have improved vastly over the last year”

Interviewer: “Okay then, tell us about it.”

Gene: “To start with, the goal is to reach LLO with 10 tons of cargo, but that actually means that the rocket has to be closer to a 1000t, at our current rocket technology. Better engines would mean lower rocket weight. The last time we had a major breakthrough, it even cut the weight in half. For now though we are looking at the 800-1000t range.”

Gene: “One major update to our designs was the RCS. For a long time, actually since we first reached orbit, we have used hydrazine. Now, that has changed. We are now changing into a Aerozine50/NTO mix. Aerozine is a better fuel, and it doubles the thrust power of the RCS and increases the isp value of the engines by some 30-40 points, which improved the fuel efficiency quite a bit.”

Gene: “The RCS are also improved by two tech levels, a impressive boost compared to the simple basic. In addition, we have also moved from a single set of large RCS to two sets of half as large RCS. This improved the manoeuvrability a fair bit. ”

Gene: “One huge benefit from this, is that we can remove hydrazine tanks from the designs. This makes designs easier, and it ends the continual problem of guestimating how much hydrazine to standard engine fuel, that rockets should have. Which would otherwise mean either useless extra weight, or, in case of too little hydrazine, that we lose the ability to start the engines. A constant point of discussion at design meetings. Happy to see it gone”
Interviewer: “Quite interesting, I can see how that is helpful. Any other recent designs changes?”

Gene: “Oh several. Another problem we have struggled with is lack of thrust in transfer stages, and to a lesser degree, in probes. By now, we have started just adding more Astris engines. In the center, we then have a single small decoupler and a structural element connecting that to the lower parts of the rocket. Such a minor fix, but still once we got around to it, launching heavy missions became much easier. Current designs will now have a minimum TWR of 0.5.  ”

Interviewer: “Not bad, anything else, other struggles?”

Gene: “Yes, we call it the  Main vs circularization stage % problem. The main stage is the first stage, which lifts the rocket into space at about 250km, and starts the circulization, while the circulation stage performs the long work of achieving orbital velocity.”

Gene: “Usually, we don’t have any problems with this, but in these heavy rocket designs, its getting difficult finding our of much of the fuel and engine mass should be in the first step, and how much in the latter. As an example, if the main stage is too small, then the rocket won’t reach 250km in altitude, and the orbit will fail. If too large, then the existing launch ode will result in the rocket being sent into much to high apoapsis. Which eventually leads to other problems.”

Gene: “On the other hand, the circularization stage needs to be strong enough to get the rocket up to orbital velocity. So it needs to have sufficient fuel en engine thrust to achieve that goal. Anyways, its a optimization problem, unfortunately finding the optimal solution takes a lot of processing time.”

Interviewer: “You also mentioned…”

Advertisements

4 comments

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s