[Note: this is a blog post version of a whitepaper we recently sent out describing the technical idea that is at the heart of the Altius business plan I pitched at the 2011 NewSpace Business Plan Competition.]
A key missing capability that is needed to enable commercially competitive research and development on space stations like the ISS is the ability to send and receive short lead-time just-in-time packages. The current long lead-times for space station deliveries make it challenging for station researchers and manufacturers to compete commercially with terrestrial counterparts. While many companies are currently developing small rockets capable of lifting payloads of the right size class to low-earth orbit (LEO), this does not serve the critical space station user need for just-in-time deliveries because these vehicles lack the capabilities needed to safely approach the station by themselves. Specialized delivery vehicles like Progress or ATV possess the capabilities needed to safely approach the station, but they cannot be affordably scaled down to the size that these small rockets can lift while leaving any useful payload. Altius Space Machines is developing a solution for this missing capability called the Direct to Station (D2S™) delivery system, which will enable small launch vehicles to safely deliver just-in-time cargo directly to the ISS, without the need for separate, proximity-operations-capable delivery vehicles.
D2S Technical Description
The Altius D2S delivery solution has two principal subsystems: a station-based guidance and control system, and an extremely-long, station-based Sticky Boom™ capture mechanism. Sticky Boom uses a compliant electroadhesive gripper that can adapt itself to the geometry of any space object and then adhere to its surface, regardless of surface material, using controlled electrostatic forces. This gripper is mounted on the end of an extremely long deployable and steerable articulated boom, which is capable of matching speeds with visiting objects over a much wider range of relative velocities than traditional robotic arms.
As shown below, (1) as a rocket upper stage approaches the station exclusion area, (2) the D2S guidance and control system tracks and performs relative navigation for the incoming rocket stage, and then (3) sends the stage thruster commands enabling the stage to use its own propulsion systems to approach close enough for (4) the D2S Sticky Boom to capture it and reel the payload in to the station. By offloading the fine-control positioning to the electromechanically articulated boom, the coarse-control capabilities of the rocket upper stage become adequate for its portion of the task.
Illustration of D2S Concept of Operations
Additional Applications of D2S
Large-Scale Direct to Station Deliveries: D2S can also be scaled-up to handle deliveries from EELV-class launch vehicles such as Atlas V, Delta IV, or Falcon 9. With the Space Shuttle now retired, D2S can reinstate the capability of delivering large replacement parts or expansion modules using existing launch vehicles without requiring the development of space tugs or the installation of expensive proximity-operations upgrades to the EELV upper stages.
Propellant Depot Resupply: The same techniques can also be used to simplify the delivery of propellant in simple, passive containers to future propellant depots, or enable the integration of large space exploration vehicles in LEO before departure to deep-space destinations.
Nanosat/Microsat Launch Anchor Market: By enabling steady demand for space station deliveries by nano- and micro-scale launch vehicles, D2S can provide an anchor market for these launch systems. This market is potentially bigger than the current small satellite launch market increasing the potential for several healthy launch providers in this payload class.
Vehicle Return Assist: The D2S hardware can also simplify the departure of sample return vehicles. By releasing the return vehicle far below the station, with a slight amount of backward velocity, the vehicle enters a trajectory that will never re-intersect with ISS. This can greatly reduce or eliminate proximity-operation requirements for such vehicles.
D2S Departure Assistance Illustration
- Develop relationships with relevant NASA groups to promote understanding of D2S.
- Work with ISS Visiting Vehicles Group to determine the best way to implement D2S to ensure safety while minimizing the overhead placed on visiting nanosat and EELV upper stages.
- Work with station researchers and manufacturers to better understand their logistics needs
- Interface with Nanosat Launch Vehicle developers to ensure their vehicles are designed from the outset to be D2S compatible.
- Work with partner companies to analyze flight dynamics, and determine Sticky Boom system design requirements.
- Develop Sticky Boom hardware including an arbitrary-geometry-capable gripper and an extremely long-reaching storable articulated boom crane system based on NASA technology.
- Space qualify and flight test the D2S system including abort operations
- Develop standard procedures for qualifying new upper stages for D2S delivery
- Work with ISS National Lab to remove any other obstacles to short lead-time deliveries.
Up to now, I was under the impression that the Sticky Boom would merely be extendable and pivot in two directions on a base. However, here you’ve mentioned making it articulated – you guys planning on throwing a few Canfield joints into the mix?
Well, for some sticky boom applications, a single-member “base gimballed” option makes a lot of sense, and is still our baseline. But for this application, where the boom may need to be 50-200m long…the boom would have to be super-thick to not want to flex like a noodle. Which is why we’re looking at something more sophisticated.
The first thing that springs to mind is to have a trio of booms in a triangular base pattern, with their guides set in such a way that when they uncoil they are hooked in to each other on one edge; the central portion (viewed head on) would approximate a triangle. That way, if one or two want to flex the third one will resist.
Have a number of questions for ya – let me know if these are answered somewhere already.
What payload sizes are you anticipating for the initial operational capability? What companies are developing the rockets that have the capability to reach ISS orbit with these payloads? When are these anticipated to be operational?
What’s your thought on getting NASA on board with small rocket upper stages navigating to within 200m of ISS? Definitely seems like a very large hurdle to overcome. Wouldn’t they want any rocket to be qualified to some level? They are VERY protective of ISS… Have you received any indication from people at NASA that they would remotely consider this sort of thing?
Good questions. Let me try and give some quick answers:
1- For the initial D2S capability we’re probably talking about likely payloads in the 10-100kg class. We’ve been talking with several companies including Ventions LLC, XCOR Aerospace, Generation Orbital, Masten, and have shared materials on the concept with a few others (Garvey, Dynetics, Masten, Virgin, etc). We’ll probably also try to reach out to the teams working on the DARPA ALASA program. Most of these groups are looking at operational timeframes in the 2014-2015 (or later) timeframe. Which gives us time to work with them both to make sure their systems are compatible with ours, and also to give us time to get our systems developed, qualified, and flight tested. Right now, we’re trying to have this operational sometime before mid 2015, but that’s a very early estimate that will likely change as we get more info (and as we try to find ways to pull that availability date in sooner).
It should be noted that there are other Sticky Boom-related opportunities that we’re trying to keep open in case we the Nanosat Launch Vehicle companies run into delays.
2- We’re getting our ducks lined up in a row for initial conversations with NASA folks in the ISS Program Office and Visiting Vehicles groups. We’ve talked with several groups that have done ISS prox-ops, and while they have said that they think we have a technically viable solution, we all know that getting NASA approval isn’t going to be trivial, so we’re trying to get the conversation started as soon as we can, so we can get to a good understanding of what we need to do to get to a yes. And also to make sure we can design in safety from the start. We’ve identified some of the challenges we’ll need to overcome, but we want to get the idea in front of NASA’s personnel to make sure there aren’t any big challenges we haven’t planned for yet.
Should also mention that we’ve been looking at intermediate (non-ISS) destinations for trying out D2S. This would be both for demo/debugging purposes, and even to prove out the market need in a lower-regulatory-burden environment. More on that later.