When Elon Musk of SpaceX tweets something interesting, it creates a wave of excitement. When he tweeted recently that SpaceX might be working on a path to retrieve the upper levels of its missiles, it triggered a string of intriguing responses.
SpaceX will attempt to deduct rocket speed from orbital velocity with the help of a giant party balloon
̵1; Elon Musk (@elonmusk) April 15, 2018
SpaceX has its lower stadiums for some time now, and it has lowered the cost of launching payloads into space. But that's the first indication that they might try to do the same with higher levels.
Twitter responders wanted to know exactly what SpaceX has in mind and what a "huge party balloon" could be. Musk has not worked out yet, but one of his Twitter followers had something interesting to add.
Quinn Kupec, a student at the James Clark School of Engineering at the University of Maryland, tweeted Musk:
If you suggest something I think you're an ultra-low ballistic entry-level, then you should and @SpaceX let's see what we have at @UofMaryland . We've been working on this for some time and have just completed some tests pic.twitter.com/nJBvyUnzaK
– Quinn Kupec (@QuinnKupec) April 16, 2018
Universe Today has joined with Mr. Kupec in Connected to see if he could help us to understand what Musk might have come up with. But first, a little background.
An "ultra-low ballistic entry-coefficient retarder" is a bit like a mouthful. The ballistic coefficient measures how well a vehicle can overcome air resistance in flight. A high ballistic coefficient means that a reentry vehicle would not quickly lose speed and reach the earth at high speeds. An ultra-low ballistic intake coefficient retarder would quickly lose speed, meaning that a vehicle would drive at low subsonic speeds prior to reaching the ground.
In order to recover an upper stage amplifier, low speeds are desirable because they produce less heat. But after Kupec there is another problem that needs to be overcome.
"What happens if these things slow down to landing speeds? If your center of gravity is well behind your midpoint, as it would be on a return If the center of gravity of the reentry vehicle is too high, it can be inverted, which is obviously not desirable The trick is, then, the speed of the entry vehicle to the point where the heat generated by the re-entry does not damage the repeater, without causing the vehicle to reverse or otherwise becomes unstable. This is not a problem for the main stage booster that SpaceX is now routinely recovering; They have their own retro rockets to control their descent and landing. But for the upper-stage boosters that reach orbital speeds, it's an obstacle that needs to be overcome.
"My research focuses specifically on how much you can push the center of gravity and still maintain the right flight configuration," said Kupec
But what about the "giant party balloon" that Musk tweeted about?
Musk could relate in color to what is called ballets. The word is a combination of the words balloon and parachute. They were invented by Goodyear Aerospace in the 1950s. They can prevent the descent of vehicles and ensure stability during descent.
Universe Today contacted Professor Dave Akin from the University of Maryland for some insights into Musk's tweet. Professor Akin has been working on reentry systems for more than two decades.
In an e-mail exchange, Professor Akin told us, "Concepts have been proposed to attach a large balloon to a cable that is pulled behind you as it enters." The balloon lowers your ballistic coefficient, which means that They slow down more in the atmosphere and heat load is lower. "So the key is to scrub your speed before you get closer to Earth, where the atmosphere is thicker and generates more heat.
But according to Professor Akin, this will not be easy. "In order to achieve the two orders of magnitude reduction in ballistic coefficient that Elon used to talk about, the balloon would have to be 120 feet in diameter, made of high-temperature tissue, so it will not be that easy."
But Musk's track record shows he does not shy away from things that are not easy.
The procurement of rocket stages is not just about lowering start-up costs, but also about space debris. The European Space Agency estimates that there are more than 29,000 space debris orbiting the Earth. There were already some collisions and accidents, with some satellites being pushed into different orbits. In 2009, the communications satellite Iridium 33 and the degraded communications satellite Russian Cosmos 2251 collided and destroyed both. If SpaceX can develop a way to get its top-level boosters, it means less garbage and fewer potential collisions.
There is a clear precedent for using balloons to manage reentry. With people like Professor Akin and Quinn Kupec, SpaceX will not have to reinvent the wheel. But they will still have much to do.
Musk tweeted another thing shortly after his "Giant Party Balloon" -Tweet:
And then land on a bouncy castle
– Elon Musk (@elonmusk) April 16, 2018
Not a word, what that could mean.
SpaceX wants to try to recycle more Falcon 9 rocket