By Jonathan Goff
President and CEO
Altius Space Machines
Part 1 of 2
It has been a while since our last blog post, and those of you have been following the news over the last month may have noticed that Altius has recently been awarded or selected for negotiation on a few significant NASA technology development contracts. These four contracts are:
- ISS Launched Cubesat Demonstration of Variable-Drag Magnetoshell Aerocapture – an SBIR Select Phase I that MSNW LLC of Redmond, WA is priming with Altius as subcontractor
- Multi-purpose Interplanetary Deployable Aerocapture System (MIDAS) – an SBIR Select Phase I that Altius is priming with MSNW LLC as subcontractor
- Kraken Asteroid Boulder Retrieval System – an Asteroid Redirect Mission BAA Phase I that Altius is priming with support from Boston-based Empire Robotics, Dr. Brad Blair of NewSpace Analytics, and the Materials Technology Lab at Lockheed Martin Space Systems in Littleton, CO
- Multipurpose SEP Module for ARM and Beyond – an Asteroid Redirect Mission BAA Phase I study where Altius will be supporting an industry team led by ExoTerra Resources of Littleton, CO.
Doug Messier of Parabolic Arc did a great job of sleuthing out what little publicly available information NASA provided on the two SBIR contracts, but the NASA announcement for the Asteroid Redirect Mission award last week provided only a little information about those contracts. To help remedy some head scratching about what this all means, in this and a subsequent blog post I’d like to introduce the technologies we’ll be researching in these contracts and provide some of my thoughts of how these potentially tie into the big picture.
We’ll start with the two SBIR contracts in this post, and discuss the two ARM BAA contracts tomorrow.
Magnetoshell Aerocapture (MAC) Technology Background
The two SBIR contracts mentioned above are both related to MSNW’s Magnetoshell Aerocapture (MAC) technology, so before I discuss those projects I would like to first give a layman’s introduction to how MAC works, and why the underlying technology is so fascinating. For more detailed explanations, you can refer to their NIAC Phase 1 Final Report and Presentation.
At its simplest level Magnetoshell Aerocapture is a method for slowing a spacecraft by using interactions between neutral gas molecules in the atmosphere and a plasma magnetoshell you create around your spacecraft. Unlike other methods of using the atmosphere to slow down, which involve deflecting the gas particles around your spacecraft, plasma magnetoshells basically absorb incoming neutral particles and then reemit them later after they’ve been brought to the same speed as the spacecraft. As the absorbed particles are accelerated to the spacecraft’s velocity, the spacecraft’s momentum is decreased at the same time.
The plasma magnetoshell is somewhat like a miniature planetary magnetosphere created around your spacecraft using a dipole electromagnet and a plasma generator. The dipole electromagnet is analogous to the earth’s magnetic field, and the plasma is injected and trapped by the dipole field. The plasma magnetoshell interacts with neutrally charged atmospheric particles via a charge exchange collision, where an electron jumps from the neutral molecule to an ion in the plasma that gets too close. At the typical velocities and densities for MAC charge exchange collisions dominate the other plasma effects, such as ionization.
The slow moving atmospheric gas particle is now an ion inside a fast-moving magnetic dipole field, which will trap it and accelerate it. The now neutralized magnetoshell ion drifts off with a velocity that is on average equal to the velocity of the spacecraft. At the right altitudes (between about 85-150ish km), the “magnetization parameter” is optimal and with the right magnetoshell plasma density, and the right magnetoshell diameter, you can guarantee that every neutral atmospheric particle that passes through the magnetoshell will be charged, captured by the magnetoshell’s dipole magnetic field, accelerated to the spacecraft’s velocity, and then neutralized when hit by a subsequent atmospheric neutral particle or eventually lost.
A couple of key benefits of plasma magnetoshells compared to other aero-deceleration approaches:
- The effective diameter of the brake can be varied rapidly by changing the current flowing in the dipole electromagnet. This can allow closed-loop control of the drag force even in the face of unknown atmospheric density variations.
- The effective diameter of the brake can be very large (up to 100 m in diameter) with respect to the spacecraft. This allows ballistic coefficients an order of magnitude or two lower than that of even inflatable entry systems and many orders of magnitude less than solid heat sheilds.
- By providing very low ballistic coefficients the atmospheric density needed for effective braking can drop by one to two orders of magnitude, directly decreasing the dynamic pressure and heating felt by the spacecraft. Studies showed a potential 14,000X decrease in heating
- The spacecraft being aerocaptured or aerobraked does not necessarily need to be aerodynamically shaped.
- Magnetoshell aerocapture does not require superconducting electromagnets, and can be performed using normal magnets powered off of a high power battery pack.
- Plasma magnetoshells may also be useful for protecting a spacecraft from high-energy particle bombardment from planetary radiation belts and solar flares.
MSNW was supported by NASA during 2012 and 2013 to evaluate this technology as part of a Phase I contract for the NASA Innovative Advanced Concepts (NIAC) program. During the Phase I, they analyzed the use of Magnetoshell Aerocapture (MAC) technology for unmanned missions to Neptune and manned Mars missions, showing in both cases huge savings in the required system masses compared to traditional propulsive capture maneuvers or traditional heat-shield aerocapture methods. More importantly, MSNW also performed proof-of-concept demonstrations of the MAC technology in a vacuum chamber at their Redmond, WA facility, which they use for testing electric propulsion systems (picture shown above). They found an over 1000X increase in drag when the magnetoshell system was operating compared to the drag caused on the system without it being activated. As David Kirtley of MSNW put it, most plasma physics ideas he’s seen tried out over the years don’t work as expected the first time they’re tried in the lab, but this worked straight out of the box.
With that background, we can now discuss the two SBIR contracts.
ISS MAC CubeSat Demo
The first of the two SBIR Select Phase 1 contracts is to design, build, and flight demonstrate the MAC technology using a 3 or 4U CubeSat deployed from the ISS. The flight test should accomplish several goals, including:
- Demonstrating the MAC technology in a space environment.
- Demonstrating the ability of the MAC system to actively control drag by varying current in the MAC electromagnet coil.
- Evaluating the impact of relative alignment of the magnetoshell dipole field and the velocity vector on the drag force created.
- Evaluating the ability of MAC to provide radiation shielding from van Allen Belt Radiation (stretch goal).
This contract will be led by MSNW, which will be developing the MAC payload systems (plasma generator, gas feed, and electromagnet coil), and Altius which will be developing the CubeSat bus (including structure, power, avionics, sensors, etc.) and integrating the MAC hardware into it. In Phase 1, MSNW will mature the design of the MAC plasma generation system, and Altius will be design the thermal interface between the MAC coil and the spacecraft.
The thermal interface design is important because the MAC coil can pull up to 1kW of power during operation, and as much of the waste heat as possible needs to be radiated to space and insulated from the rest of the spacecraft to avoid damage to the spacecraft electronics or batteries. In case you’re wondering, 1kW of power is a fairly insane amount of power for a CubeSat. I’m not positive, but the 250W-hr Lithium-Ion battery we have baselined may be the biggest battery that has ever flown on a CubeSat this small.
If all goes well, in Phase 2, our two companies will be doing detailed design and production of flight hardware, with the goal of having hardware designed, built, integrated, tested, shepherded through the Payload Safety Review Process (with help from NanoRacks LLC) and ready for delivery to the ISS by the end of Phase 2.
MIDAS: Braking and Power (and maybe Comms) to the Interplanetary CubeSat People!
The goal of the Altius-led SBIR Select Phase 1 contract is to develop a multi-purpose system that addresses three of the biggest challenges for using CubeSats for interplanetary missions—propulsion, power, and communications.
The MIDAS system combines three deployable elements using common STEM booms for deployment:
- A compactly-stowable, large diameter (2-5m) electromagnet coil for a MAC system capable of aerocapture around Mars, Venus, or Outer Gas Giants.
- One or more high power density rollable thin-film solar arrays capable of providing plentiful power to a CubeSat even out past Mars orbit.
- An integrated deployable earth return communications antenna that can enable closing a useful communications link with Earth.
Increasing the coil diameter can significantly increase the diameter of the plasma magnetoshell, even if you hold coil mass and battery power constant. This would enable a CubeSat with a MIDAS system to perform aerocapture maneuvers around any solar system body with an atmosphere. Another potential benefit of having the MAC electromagnet coil deployed on the end of long booms is that since the booms do not have to be equally sized, it may be possible to create a dipole magnetic field whose axis does not pass through the spacecraft itself, which may potentially reduce or eliminate particle impingement on the spacecraft when the MAC system is used for radiation shielding.
The rollable thin-film solar array work builds on research performed over the years by several US and European entities, including composite STEM boom developers RolaTube and Roccor, whom Altius has worked with in the past. Previous work on this type of solar array has mainly focused on very large arrays for large-scale, 100kW-class solar-electric propulsion vehicles, but this will be the first attempt at using the technology on a CubeSat scale. With luck this may even be the first flight demonstration of rollable thin-film solar arrays in space. While thin-film flexible solar cells are not quite as efficient as more traditional solar cells, they are improving fairly rapidly, and the available surface area should enable orbit-averaged power levels >200W in Earth orbit, and >100W in Mars Orbit, both of which are fairly significant for a CubeSat system.
In Phase 1, we’re going to be initially selecting one or two missions to serve as the design point for the MIDAS hardware. MSNW will then help us analyze the MAC system and size a MAC electromagnet coil. Altius will design the deployable structure to react drag loads from the MAC electromagnet coil during operations, and will design the deployment method for the booms and coil. The goal is to find a way to package the booms, solar arrays, coils, antenna (and the plasma generator and battery) into ~4U of space, leaving 1U for avionics and 1U for a payload. This will be an exercise in cramming 10lb of stuff into a 5lb bag, but that’s par for the course for most CubeSat projects. If all goes well in Phase 1, Phase 2 would be focused on designing and building flight hardware for the MIDAS system. If we also win the ISS MAC Demo Phase 2, we may try to incorporate the MIDAS hardware into an actual flight 6U cubesat design for flight test either from ISS or deployed from a rocket in a GTO or higher orbit.
While the SBIR work will be focused on a CubeSat-scale version, the concept of using a deployable electromagnet coil to enhance MAC performance makes a lot of sense for larger systems as well, such as planetary science missions, enabling capsules such as the Orion MPCV to return from higher-velocity destinations such as Mars or NEOs, and potentially enabling recovery of rocket upper stages.
How You Can Be Involved
Now that the contract has kicked-off, we will be trying to select one or two missions to serve as the point-of-departure for analyzing our MIDAS hardware. As time permits, either I or Dan Copel, the MIDAS Principal Investigator will try to publish periodic blog posts to keep people updated on how things are going. If you’re involved with a group that’s currently working on interplanetary CubeSat missions, we’d love to talk with you about potential missions that could use our MIDAS technology!
Coming Up Next: Asteroid Redirect Mission Phase I Contracts (aka Release the Kraken!)