The problem is getting a compact throttlable rocket engine. While you can throttle solid rocket motors[0], the solid rocket motors you can buy at your local hob

The problem is getting a compact throttlable rocket engine. While you can throttle solid rocket motors[0], the solid rocket motors you can buy at your local hobby shop would not be very good for this, as they don't burn for very long. Hybrid rocket engines might be the thing to use for this and amateurs have built such things[1]. [0]https://www.youtube.com/watch?v=W8efpDBvTDE https://www.youtube.com/watch?v=W8efpDBvTDE [1]https://www.youtube.com/watch?v=X5o4LIZ3i4o#t=23 https://www.youtube.com/watch?v=X5o4LIZ3i4o#t=23