Marianne Dyson, December 2018
Considering that we are celebrating the 50th anniversary of Apollo, and that NASA has contracted with Firefly Aerospace and Intuitive Machines to provide new lander vehicles, I thought you all might enjoy this article I wrote that was originally published in Ad Astra in 2013.
Every year at space conference parties, enthusiasts have pondered the question: If we flew an Apollo mission to the Moon with today’s technology, how would it be different? One enthusiast, five-time shuttle astronaut Jeff Hoffman, PhD, who is now a professor at MIT, assigned a couple of graduate students to find a definitive answer.
The students, Alex Buck and Austin Nicholas, presented their findings at the Brown University-Vernadsky Institute-MIT Microsymposium 54 held the Sunday before the annual Lunar and Planetary Science Conference in Houston in March 2013. Though Dr. Hoffman wasn’t able to attend (he answered questions via telecom), Apollo 15 Moonwalker Dave Scott was present to enthusiastically endorse their work and encourage the space community to act on it.
The study focused on using the basic Apollo architecture of a command and service module (CSM) to launch from and return to Earth, connected to a lunar module (LM) to go to and from the lunar surface with modifications made possible by current technology.
Technology upgrades to the lunar lander included higher efficiency propellants, lightweight materials for the structure, and state-of-the-art electronics for computing, avionics, and communications. The electronics provide “on the order of a billion-fold increase in terms of reduced power consumption and increased computing capability,” the students said. They also replaced the Apollo-era batteries with modern fuel cells that produce water as a useful byproduct.
The results were astounding. “We could cut up to 40 percent of the lunar module mass while still maintaining the same payload capability of the original lunar module.”
Landing Vehicle Comparison
HALOs Lunar Lander
|Payload Mass||500 kg||2300 kg||1200 kg|
|Sample Return Mass||100 kg||350 kg||700 kg|
|Crew to Surface||2||3||3|
One problem with switching to cryogenic fuels for the Human Architecture for Lunar Operations (HALOs) lander is that the fuel tanks, which are between the descent engines and the crew cabin, are, like the space shuttle external tank, enormous. The students noted, “This makes surface operations very difficult because it puts the crew habitat and the ascent stage and payload really high above the surface.” So the young engineers asked, “What if you didn’t have to land on top of the descent stage?” Why not eject the descent stage a few kilometers above the surface and finish the landing with the ascent stage? They found the cost in propellant is minimal, and the two-ton descent stage provides the bonus of a fresh impact crater for study about 5 km (3 mi) from the HALOs lander.
Next, the students looked at landing constraints. “All of the Apollo landing sites were on the Nearside and in the equatorial region,” the students said. “If we want to get some increased return out of a future landing program, it wouldn’t really make sense to go back to all those same spots.” But, “to reach high-latitude sites near the pole requires a lot of plane change to come in from Earth and return to Earth,” they said.
An elliptical polar “parking” orbit for the CSM solves the problem. “Plane change maneuvers have a fuel cost proportional to the speed at which you’re going when you do the maneuver,” the students noted. Like comets speed up when close to the Sun and slow down farther away, “that speed is lower the farther away you are in your orbit. So making the orbit highly elliptical reduces the fuel cost of those maneuvers and thus the mass of the entire system.”
Because these elliptical orbits are so efficient, using them can save 30-50 percent of launch mass compared to not using them.
However, “We don’t have a single launch vehicle that can launch a monolithic Earth departure stage to take this much mass to the Moon,” the students said. “So you have to lift the system in several pieces and assemble them in Earth orbit.” They assumed one Delta 4 Heavy and two Falcon Heavies, and used a SpaceX Dragon capsule for the CSM. The different parts would then be assembled after an Earth orbit rendezvous (EOM), something that has become a routine part of space station operations.
The CSM and LM are attached to a Lunar Orbit Insertion and Descent (LOID) stage (that would be ejected just before landing). The LOID puts the CSM into an elliptical lunar orbit about one by 10 lunar radii. “The CSM stays there while the LM goes to the Moon.”
Unlike Apollo, all three crewmembers would land. How long they stay depends on how much luggage they bring, and how many souvenirs they take home. “If you want to do a seven-day surface mission, you can bring a payload with you to the surface of over 2,000 kg (4,400 lbs) and return 350 kg (770 lbs),” the students said. The total mission from launch to landing would last about two weeks.
“For a 14-day surface stay, you can bring just over 1,000 kg (2,200 lbs) to the surface and return 700 kg (1,500 lbs) back to Earth.” The increased sample return is based on the steady collection rate of 50 kg/day (110 lbs/day). The total mission duration would be about three weeks.
Luggage might include an Apollo rover at 210 kg (460 lbs) with an 8 km (5 mi) range, or a souped-up Constellation pressurized chariot at 1,000 kg (2,200 lbs) with a 100 km (62 mi) range. An Apollo lunar surface experiment package (ALSEP) would take up 166 kg (365 lbs).
After lunar surface operations, the LM rendezvous with the CSM for return to Earth. (As in Apollo, the LM is discarded after use, but the students said future studies could examine the possibility of reusing the LM by “parking it at a gravitational semi-stable point such as L2.) The CSM parachutes into the ocean like the Apollo capsules did.
“We think you can go back to the Moon with people without needing a super-heavy launch vehicle,” the students concluded. “We can do that while improving our payload capability and surface stay duration. And, we allowed the capability of putting humans and payload anywhere on the Moon.”
When asked where they’d personally like to go, the students answered with a smile, “Mars!”
Holiday Space Gift Ideas
Perfect stocking stuffer that benefits the International Women in Aviation and Space Museum: Women in Aviation and Space Playing Cards! Yours truly is the Ace of Clubs.
For high school and up, give a positive vision of the future, a gift membership in the National Space Society. Read my article, “Chinese Planetary Exploration Plans” in the 2018-4 (current) issue of Ad Astra magazine.
For future astronauts and lunar pioneers, get a copy of To the Moon and Back: My Apollo 11 Adventure, a pop-up book coauthored with Buzz Aldrin with art by Bruce Foster, and 2017 Best STEM Book, Welcome to Mars: Making a Home on the Red Planet.
For middle school and up, consider a gift print or electronic subscription to Analog Science Fiction magazine. My science fact article, “In Defense of the Planet,” is in the Nov/Dec 2018 issue. Also consider a copy of my stories, most previously published in Analog, Fly Me to the Moon.