Back when I left Masten to start Altius, I originally thought I was starting a launch vehicle company focused on reusable nanosat launchers. While we pivoted away from that to focus on space robotics, I’ve continued to dabble with a smallsat RLV concept that I started developing from ideas from this blog back while I was still at Masten. Since we’re definitely not in the launcher business at this point, I wanted to share the idea in the hopes that at least some of the crazy ideas get picked up by someone at some point. Without further ado, I’d like to introduce you to the Boomerang Air-Launched TSTO RLV.
What is Boomerang?
Boomerang is a concept for a low-cost, eventually fully reusable, two-stage to orbit launch system. Boomerang had the following three main system elements, which will be described in more detail in subsequent blog posts:
- A subsonic airbreathing carrier aircraft
- A glide-forward recovery liquid rocket powered first stage
- A hypersonic plasmadynamic decelerator-recovered liquid rocket powered upper stage
All three components are designed to return for a precision landing at the originating air-field, with design decisions that should optimize the probability of gas and go reuse.
- The two rocket stages are prepped horizontally and integrated with the planned payload to the carrier aircraft at the originating airfield.
- The carrier aircraft then takes off and heads up-range (ie in a direction opposite the desired launch azimuth). Once the carrier aircraft is far enough up-range for a glide-forward return, it turns around and preps for launch.
- The aircraft then begins to pull-up. As it nears the attitude where it can no-longer retain airspeed, the first stage begins igniting engines (what I call a “Gamma Maneuver”, although like many of my good crazy ideas, John Hare and Kirk Sorensen both beat me to the punch), enabling the aircraft to continue increasing its flight path angle to the optimal separation angle. Crossfeed from tanks on the carrier aircraft keep the first stage topped.
- Immediately prior to separation, the crossfeed disconnects are separated, and the rocket vehicle “drops” the aircraft off its back, and immediately begins throttling its engines up to full flight power.
- The first stage then performs a burn to near the optimal staging altitude and velocity. After the upper stage is released and on its way, the first stage can perform a braking burn if necessary or could potentially use a hypersonic plasmadynamic decelerator (more on that later) for some of the braking depending on what reentry speed limit minimizes the reuse complexity.
- The upper stage continues to orbit and delivers its payload as with a typical launch vehicle.
- The first stage glides forward toward the landing site. Once in the general vicinity it performs a course correction maneuver to approach the originating airfield. It then lands using either vertical or horizontal powered landing, or via an autogyrating helicopter system (still an open trade).
- After delivering the payload to orbit, the upper stage waits for the originating airfield to pass under its ground track again, then performs a retro-burn, and uses a hypersonic plasmadynamic decelerator to slow itself down sufficiently for safe recovery. Recovery at this point could be via mid-air recovery, horizontal powered landing, or autogyrating helicopter landing.
- Lather, rinse, repeat.
High Level Benefits of This Approach
While this isn’t the most orthodox approach to air launch, and does include some key, non-trivial challenge areas, it has a lot of benefits I like:
- The Gamma Maneuver enables launching at high subsonic speeds and flight path angles without requiring a military aircraft for launch. This can knock over 1000m/s of gravity and drag losses off of the system, which makes a huge difference for a small rocket. The gamma maneuver may also eliminate the need for large aerosurfaces or structures to accommodate large bending loads as is a traditional challenge for drop-and-light air-launched rockets.
- VTVL with glideforward recovery means that staging can take place at a closer to performance optimum stage velocity than is possible with boost-back or glide-back systems, since you don’t have to completely kill and then reverse first stage velocity. At worst you have to decelerate a little to make recovery easier. These two items greatly decrease the performance hit of recovering the first stage.
- The Gamma Maneuver with crossfeed also enables launching the rocket nearly full after having checked out all of the engines sequentially for several seconds prior to separation. Why on earth would you drop a reusable rocket before making sure its engines were all operating nominally if you could?
- While they’re still a low TRL technology, hypersonic plasmadynamic decelerators (HPDs, another name for MSNW’s Magnetoshell Aerocapture technology as applied to aeroentry) may greatly simplify upper stage recovery if they pan out. While they don’t give a lot of cross-range maneuverability, they do allow pretty precise up/down-range targeting, and might eliminate or at least greatly reduce the need for TPS on the upper stage.
- Boomerang can be initially flown with an expendable upper stage, with the HPDs added as a post-delivery experiment kit, allowing upper stage reuse to be tested-out gradually.
- If the stages are recovered via horizontal landing (rocket powered, mid-air recovered, or autogyro landed), that would make reintegration with the carrier airplane even easier, potentially eliminating the need for any complex restacking launch infrastructure.
Key Challenge Areas
Obviously there are some key challenges that would need to be addressed both in the design and risk reduction phases:
- The Gamma Maneuver scares the crap out of most pilots. I have a few suggestions for how to deal both via system design and how one could do subscale demonstrations with this that I’ll discuss in follow-on blog posts related to the carrier plane and first stage.
- A related issue is separation dynamics with a lit rocket vehicle. I’ll discuss this a bit in the post on the first stage.
- Another related issue is lighting rocket engine while attached to an aircraft, for fear of hard starts. I have some ideas for how to deal with this as well.
- Storing cryogenic propellants for air-launch can be a pain in the neck. I have some great ideas for this, that I’ve discussed a bit previously, and which I’ll update in one of these follow-on posts related to the first stage.
There are a lot of nuances I probably won’t be able to get into in this series, but I wanted to lay out the concept so that if someone wants to borrow/steal ideas, they can.
Next Up in Part II: Carrier Plane Considerations and Options