DragonLab-g: an early step to Mars and beyond
by Tom Hill
|Instead of trying to adapt the human body to microgravity, why not simply generate artificial gravity along the way?|
While current efforts in space are being slowed by debates over costs, preferred methods, and destinations, there are bigger concerns for long-term space habitation. Winds of political will change for better or for worse in the span of a couple years, but two constant challenges await anyone who ventures beyond the atmosphere for a long period of time: the lack of gravity, which changes physiology with especially strong impacts on muscles and bones; and radiation, which raises the risk of cancer and has other effects over time.
The lack-of-gravity question has been the focus of NASA’s research since the end of the Apollo program. Through years of on-orbit research in the form of exercise routines and attempted medical interventions, the space agencies of the world have tried to understand the human body’s reaction to microgravity, and to find a way to counteract it.
There are those who say research so far has been trying to answer the wrong question. Instead of trying to adapt the human body to microgravity, why not simply generate artificial gravity along the way? As early as 1966, astronauts (Gemini 11 and 12) did just that, attaching tethers to their Agena docking targets, then backing away and spinning the combined spacecraft end over end. Gravity levels were low, to the point where astronauts could not feel any (artificial) gravity but a pen could be seen accelerating in the expected direction. There were some unexplained tether dynamics during deployment and spinup, but the overall approach worked. Future spacecraft such as Apollo, Skylab, Shuttle, and ISS were not built for such demonstration, and interest in the field had waned anyway.
An example of the use of artificial gravity for a mission to Mars would involve a crew capsule separating mechanically from the stage that sent it on its way from Earth. The craft would remain connected to its upper stage by a tether. Using onboard thrusters, the crew capsule would maneuver itself away from the upper stage while inducing an end-over-end spin in the system. Eventual rotation speed depends on the tether length, difference in mass between the crew capsule and the upper stage, and the desired gravity field. The system would continue to spin while en route to Mars. As it approached the Red Planet, the crewed section would separate from the upper stage, allowing precise control of the craft for Mars orbit entry and landing.
While anyone can demonstrate artificial gravity by swinging a bucket of water in a circle without spilling it, in space travel there are several questions that the Gemini missions did not answer:
|While many people decry the retirement of the Space Shuttle, it wasn’t suitable for analyzing gravity or radiation questions.|
The radiation question has also been a focus of space agency research over the past decades. However, the radiation environment of LEO (low Earth orbit), where most of this research has been performed, is different than what crews traveling beyond LEO will experience. The International Space Station (ISS) is well protected from some radiation dangers by Earth’s magnetic field. That field extends beyond LEO but loses most of its effectiveness beyond geosynchronous orbit. Getting the answers to the correct radiation questions will involve travel and long-term exposure beyond Earth’s magnetosphere.
Some questions that need to be answered related to the radiation issue include:
While many people decry the retirement of the Space Shuttle, it wasn’t suitable for analyzing gravity or radiation questions. Returning to small spacecraft allows such analysis to begin again. The craft that recently flew to the ISS is also the craft that can support both. That craft is named Dragon, and its derivative DragonLab. These spacecraft, and their second stages, provide an almost off-the-shelf solution to two of the nagging problems of long-term spaceflight. (Efforts to contact SpaceX about this idea have not been successful, although the company has been a bit busy lately.)
Part of the beauty of this proposal is the stepwise approach it allows, while also offering the possibility of meeting mission objectives with a minimum number of flights. While any of these missions could be the start, one sample progression of missions includes:
|The cost of DragonLab missions put them in reach of companies or even wealthy individuals who want to have a lasting, positive impact on humanity’s expansion into the cosmos.|
Modifications are required to flight hardware to enable these missions. Two obvious ones include strengthening the solar panels on the Dragon spacecraft and a method of rapidly passifying the Falcon 9 second stage. The solar panels are meant to be deployed in zero gravity, and only need to withstand accelerations provided by the Draco thrusters during flight. Exposure to any gravity field will likely require some sort of structural change. The Falcon 9 second stage requires passification to prevent the eventual explosive loss of propellants. This would be particularly important for operations near the ISS. Current orbital debris mitigation requirements may have driven these changes already, though timing them to take place early in a mission, perhaps with crew on board an attached Dragon capsule, will likely be new.
As stated before, artificial gravity research hasn’t been a priority with any space agency since the 1960s. It’s likely that an agency might not abandon decades of research in one direction to start off in another. This may be irrelevant since the cost of DragonLab missions (several tens of millions of dollars, though a dedicated mission would have to foot the bill for a Falcon flight into orbit as well) put them in reach of companies or even wealthy individuals who want to have a lasting, positive impact on humanity’s expansion into the cosmos.