Jack Taylor/Photo Editor
The dream of creating the world’s first fully reusable launch vehicle has been sought after for decades. The National Aerospace Plane (NASP) began the chase in the 80s with their proposed X-30 space plane. NASA and Lockheed Martin took up the cause with the X-33 in the 90’s. By 2001 the project was cancelled after only 5 years of development. The Space Shuttle was originally intended to be fully reusable. However, the technology needed to overcome the incredible thrust to weight ratios just wasn’t there.
With more advances in material engineering and more reliable composites, the dream of a completely reusable vehicle is back on the table and SpaceX has boldly taken on the challenge. Their ambitious plan includes autonomously returning the entire first stage of the vehicle to the launch site using a powered vertical landing. They are the only major company currently planning to completely reuse their vehicle, a goal which has never been successfully completed. In April 2015, United Launch Alliance (ULA) announced the Vulcan rocket. Their new design will also be reusable, but only partially, similar to the Shuttle and NASA’s new Space Launch System. They plan on recovering only the first stage engines after the payload has deployed, recovering them with a helicopter.
SpaceX and ULA are taking two different approaches to reduce the costs of their launches. It begs the question if one is better than the other. But to compare the two systems, several factors should be taken into consideration. The first question is the feasibility of recovery. The second factor to gauging success is the feasibility of repeatability. Then, the long-term cost must be assessed in order to determine if reusing the rocket will effectively reduce costs.
ULA is taking a conservative, yet feasible approach by only recovering the engine rather than an entire stage. Mid-Air Recovery (MAR) of cargo from high altitudes and from space has been used successfully for over 50 years. It was a major resource in recovering film canisters from space for the Corona Project in the 1960s. Using existing technology that is already proven is an extremely cost effective method of recovery and bodes well for success.
In order to return the entire first stage in a vertical landing configuration, SpaceX had to develop several new technologies in order to guide the vehicle to its landing site and slow it down enough to land, including restartable and throttleable engines, new attitude control systems, guidance and navigation sensors, hypersonic grid fins, and landing gear. Developing new technology is expensive and requires extensive testing. SpaceX has implemented this technology on their Falcon 9 v1.1. Two landings have been attempted and both have failed.
The feasibility of repeatability is also a huge hurdle SpaceX must overcome. Because of the extreme conditions the engines endure, they are built so strongly that they become inherently reusable. Fuel tanks do not have that luxury. This was obvious in the Space Shuttle mission. STS-133 suffered months of delays due to structural failures in the fuel tank that occurred from filling and draining the tank too many times. ULA’s cost analysis predicts that a single launch vehicle will have to be reused about 10 times before breaking even from the cost of refurbishment. To get a decent return, the vehicle would have to be flown around 14-16 times. Filling and draining a tank 10 times would create huge amounts of fatigue stress, and then the aerodynamic and dynamic stresses that occur during launch and landing must be factored in. Keeping in mind that SpaceX’s current success rate is only 10/11, the ability for one entire first stage to survive 10 consecutive launches appears deplorable at best.
ULA’s Russian RD-180 engines have already proven 4000 seconds of run time. In order to be flown three consecutive times, the engine would only have to be improved to last 4040 seconds. This proves that the current engine is already nearly capable of being flown three times with very little modification or cost. The same cost analysis that predicted 10 full stage recoveries to break even also predicts that recovering just the engine only requires reusing it twice.
Recovering an entire stage is not practically feasible nor is it economically reasonable. The weight of an engine is only 25% of the weight of the booster, yet it accounts for 65% of the booster cost. That means 75% of the weight that SpaceX is trying to recover only recovers 35% of the cost. Pound for pound, it is smarter and more economical to only recover the engine. In addition, SpaceX loses 30% of its payload capability with its vertical landing system because it uses about 3% of its remaining fuel to redirect, decelerate, and land the entire stage. Considering they are paid pound for pound for payload, a 30% reduction in carrying capacity means smaller payload and smaller contracts. ULA’s system does not incur a payload penalty, which is a major plus for economic efficiency.
SpaceX is the only organization attempting complete stage recovery, and there is probably a reason for that. SpaceX is reducing precious payload capacity, carrying burdensome amounts of extra fuel, and using it to slow down the heavy fuel tank structure that will ultimately not survive enough launches to become profitable. Even if they developed stronger structures that could survive multiple launches, ten consecutive launch and landing success is just not realistic. Out of the three planned landing, only two were attempted because of bad weather. If SpaceX plans to make their system profitable, they will have to guarantee a better success ration than 0/3.
ULA has chosen the partial recovery route because of the realistic economic returns. Without reducing their payload capacity, they will be able to reduce costs in a reliable, and repeatable recovery system with very little investment into new or unproven technology.
Maybe one day SpaceX will surprise the community with a miracle, but as of now it seems ULA has made the ‘smart’ choice.