Dr. Robert Zubrin, the thought leader and founder of the Mars Society, has developed a plan called “moon direct” that applies his Mars Direct ideals towards the Moon. It takes advantage of cheaper currently available commercial rockets to get us there sooner, cheaper and at lower risk.
Dr Robert Zubrin is best known for his Mars direct plan initially proposed in 1990 and later expanded on in his book “the case for mars” published in 1996. In Mars Direct, Zubrin proposes a series of rocket launches to place key pieces of technology on Mars in advance of a manned mission. Starting with the launch of a return vehicle and fuel production equipment, followed by launching a habitat module and then a bare bones contingent of astronauts. By living off the land and taking some risks Mars Direct would put people on Mars quickly, mostly with existing technology.
Zubrin’s approach could be summarized as “If you want to go to Mars, just focus on doing that”. With the excitement building around lunar exploration again he has taken this same direct approach strategy and developed a plan for getting to the moon.
Zubrin dislikes the NASA plan to build a lunar orbital platform and gateway (LOP-G) because it won’t lower costs of getting back to the moon or mars. In fact the gateway reduces scheduling flexibility since the unusual orbit proposed would have launch windows every 2 weeks rather than continuous. And the rendezvous in lunar orbit will add fuel costs to every mission that uses it. Instead of building a small space station in lunar orbit zubrin would prefer to skip directly to build the moon base itself.
The NASA Lunar Gateway will be a small space station in orbit around the moon. It would be placed in what is called a near-rectilinear halo orbit which would make it accessible to a large percentage of the lunar surface for possible missions.
It is not like the ISS. The Gateway is designed to be left vacant for most of the time. You could think of it as a very expensive garage to park a lunar lander. It is designed as a waypoint between earth and either the moon, mars or deep space. It would be inhabited only while there is an ongoing mission on the moon, and wouldn’t be suitable for long-term stays. On it’s own the station doesn’t provide much scientific value that can’t be had at the ISS. Indeed, since it is exposed to cosmic radiation, for safety reasons, human use of the station would be minimized. With 1 or 2 lunar missions per year the Gateway would be vacant for more than 90% of the time.
And with SLS being the only launch vehicle capable of getting humans to lunar orbit, each mission would be estimated at $2 billion. Difficult to sustain.
Instead Dr. Zubrin suggests that if we want to go back to the moon, then we should just start by going there directly and build a moon base on the surface. There is real value to being on the surface from a scientific and operational, and safety perspective. Cosmic radiation exposure at LOP-G can be mitigated by burying or digging and using lunar material as a shield. The scientific work about the moon mostly needs to be done on the moon, so putting resources into orbit invests in the wrong place. And operationally, the ability to mine lunar water is the potential game changer that makes local lunar transport feasible, reduces ongoing costs to maintain the base, and would ultimately make the moon a reasonable place to stop on the way to deep space (to refuel).
The moon direct mission makes use of SpaceX rockets to cheaply deliver payloads to the surface of the moon and it operates in a three phase process. To start, falcon heavy would land a 10 ton habitat module and supplies on the surface of the moon. Falcon heavy is not rated for human transport, so all these initial supply missions would be robotic deliveries, with a goal of providing the hardware required for subsequent missions. Zubrin suggests that the most appropriate place for a moon base is at one of the poles – where there is evidence for ample water and perpetual sunlight for solar power. With the first phase of delivery missions complete, we would move on to the next step.
The second phase would get humans to the moon to continue with constructruction and assembly of the previously launched equipment and establish the production of hydrogen fuel. The Falcon 9 does not have the thrust required to reach the moon with a crew. So getting astronauts to the moon without using an expensive SLS launch, requires some creativity. Moon Direct tackles this by suggesting a pair of launches. Start by launching a fueled lunar lander called the LEV into LEO. This lunar lander vehicle would operate as a cis-lunar transport vehicle that ferries people from LEO to the lunar surface and back. The LEV launch would be followed by a manned dragon capsule. The Dragon capsule and lander will meet in LEO, the crew will transfer to the the lander, and then the lander leaves the dragon behind and proceeds to the moon. In theory, the LEV could rendezvous with astronauts in a Dragon Crew capsule directly or via the ISS. Without the capability yet of producing hydrogen on the moon, we would also have to launch fuel ahead of any lunar mission at this stage in order to have the fuel to power the LEV for the journey back. One of the key insights here is that by not flying the earth re-entry vehicle (crewed dragon) all the way to the lunar orbit there is a massive savings in mass and fuel required. Bringing parachutes, and heat shielding to the moon is unnecessary so those are left in LEO.
The final phase of the plan would be to start using electrolyzed lunar water to fuel the lunar lander vehicle. This would eliminate the need to launch additional fuel into space, and would power the cis-lunar transit of people and supplies from earth orbit to the moon and back. It would also power the lander on hops around the moon to access areas of interest and significantly reduce the costs of future missions to the moon.
Most of the technology for making this Moon Direct strategy real already exists or can be quickly developed based off of existing hardware. The new tech for this mission is an updated hydrogen fuelled lunar exploration vehicle to land and takeoff from the moon. The apollo lander was a one time use vehicle – the landing legs were left on the surface of the moon. so for this mission we would need something fully reusable and single stage. The other things to design such as a habitat module suitable for moon gravity would be relatively straight forward engineering.
This 3 phase direct approach to the moon has a lot of things going for it.
- It gets humans back to the moon quickly
- It builds a base that has real operational and scientific value
- It would contribute to lowering the ongoing costs of transiting to the moon
- It leverages low cost SpaceX rockets rather than expensive SLS, while being flexible for using Soyuz, or other rockets as well.
- It has scheduling flexibility – can launch at anytime to or from the moon.
- Lower human risks from cosmic ray exposure than LOP-G
- Lower liability and maintenance costs than LOP-G
- Allows for long term permanently manned presence on the moon.
It’s worth taking a quick moment to break down the costs to compare the LOP-G plan with Moon Direct. Because there is a massive difference.
If we assume that the gateway platform would be roughly the same cost as the initial lunar base facility, then the difference is really down to the launch costs and ongoing maintenance costs. LOP-G would likely require 3 or more SLS launches at approximately $2B each to get the major modules into lunar orbit. Ongoing orion/SLS missions for humans would be an additional $2B each. Let’s say that is $8B + the actual cost of the Gateway station.
Moon Direct plan uses Falcon Heavy rockets at $150M each launch and Falcon 9s at $70M each. Zubrin suggests that with 2 launches we could get 16 tons of cargo to the south pole and that would be sufficient for getting started as part of phase 1. A pair of launches with Falcon Heavy to launch a fueled LEV, followed by a Falcon 9 and Dragon 2 crewed mission would be $220M and may need to be done twice to complete the base enough and establish production of hydrogen on the moon. This would put the necessary hardware and people in space for a launch cost of about $740M. This is a massive savings over the LOP-G. At approximately 1/10th the price to get established.
Ongoing costs make this difference even wider. SLS Orion missions to the Moon will continue to cost $2B each. Moon Direct will require a Falcon 9 launch at < $70M + minor costs of piloting the LEV using hydrogen from the moon. That works out to 1/25th the cost.
Furthermore, LOP-G missions would be capped at 2 week durations for the rendevous windows, but once established, a lunar base on the surface could be inhabited for many months at a time multiplying the scientific and operational value we get out of it.
Dr. Zubrin estimates that the total cost for the Moon Direct plan including the base and launches to be an initial $1.5B for phase 1 and 2 missions, plus an ongoing $420M per year for 3 human missions to swap out crews and re-supply the base. This is a real bargain compared to the LOP-G plan and well within the existing NASA budget for human spaceflight
This to me seems like a very practical plan for NASA to consider.