Going to the moon to protect Earth

Michael Nord’s article “Walking on rocket propellant” [April 2021] offers hope that the moon will have resources that all may share. In particular, if oxygen is generally available and makes up 89% of the mass for an H2O rocket exhaust, then the burden of shipping rocket propellant or water to the moon is greatly reduced. This would alleviate competition among space-faring nations for those special locations (e.g., poles) that already have water.

It has been suggested that fusion-powered rockets, using the moon’s helium-3, could provide the necessary delta-v’s of 10s of kilometers per second (over the Earth’s orbital speed of 30 km/s), to reach out quickly to defend the Earth from comets and asteroids. Such rockets would carry nuclear warheads whose flash could deflect the incoming object by means of sudden surface ablation. The very small cross-section for fusion reactions, however, means the size of a fusion rocket would totally dwarf the rather compact nuclear warhead. An alternative approach, based on so-called mass driver technology, could electromagnetically accelerate the nuclear payload to adequate intercept speeds but requires driver lengths of upward of 10 kilometers; big, but not impossible. It has the advantage of multiple shots for a single investment in mass but needs to be sited where the rotation of the moon provides an adequate sweep of the potential angles required for intercept.

This returns us to the need for planning the use of lunar real estate, even if finding and extracting water is not the compelling goal. Such planning in order to protect the Earth can be an international effort. It would be a truly exceptional engineering project, but one for which all the physical and engineering requirements are well-understood.

Peter J. Turchi
Santa Fe, New Mexico
Turchi is a fellow of both AIAA and IEEE and former president of the Electric Rocket Propulsion Society.

Giants in their fields

When they asked Isaac Newton how he could see so far, he replied, “I was standing on the shoulders of giants,” referring to Galileo Galilei. I read the article by Amanda Miller about the new satellite directed by Dr. Martin Weisskopf [“Building a new astronomy tool,” April 2021] and it reminded me of Newton’s reply. Dr. Weisskopf is building a wonderful instrument to investigate the universe following the properties of X-ray astronomy started by MIT professor Bruno Rossi. Interestingly enough Dr. Weisskopf and Dr. Harvey Tenenbaum received the Bruno Rossi Prize for astronomy in 2004.

I appreciate the thorough reporting Aerospace America produces to keep me informed and up to date on the developments in space science. Keep up the good work!

Giuseppe Aurilio, AIAA senior member
Arlington, Massachusetts
Aurilio assisted with the mechanical design of the Chandra X-ray Observatory at the Harvard-Smithsonian Center for Astrophysics in Massachusetts.

Another rocket plane design

The article “Why it’s time to reach for full reusability” grabbed my attention [May 2021]. It was very well-written and illuminated the practical and economic parameters of commercial launch operations.
The 2-stage (2-1/2 stage?) rocket plane design that seems optimal reminded me of DLR’s SpaceLiner program, spearheaded by Dr. Martin Sippel there. That program has roots in the Sanger design but has been continuously studied and refined for many years — for the purpose of closing a case for an economical, commercial, viable space transportation system.

Allan Lockheed, AIAA senior member
Golden, Colorado

“Doom and gloom” commentaries

Regarding the April 2021 Aerospace America issue, I found the commentaries [“Our role in assuring a cleaner, greener future,” and “Decarbonizing by 2050: optimists, pessimists and realists”] frustrating. I have studied this subject area for decades and clearly realize how this subject is being used to advance a political agenda not based on solid, real science. It’s perfectly fine for AIAA members to explore alternative energy solutions, but it needs to be for the right reasons and not from some hysterical doom and gloom. Your commentaries give credence to this gloom and doom and don’t help anyone.

Martin Machniak, AIAA member
Chula Vista, California

Going to the moon to protect Earth