July 2003
Meetings with Congress
This past month, we spent a lot of time meeting with key members of Congress and their staffers regarding space related legislation. Our primary concern is ensuring that the regulatory structure governing the embryonic commercial launch vehicle industry strikes a reasonable balance between public safety and a healthy launch industry.
In particular, I was fortunate enough to spend considerable time with Congressman Rohrabacher, Chairman of the House Space and Aeronautics Subcommittee, and Senator Brownback, Chairman of the Senate Space Subcommittee. My assessment is that there is a genuine appreciation on the part of the Congressional space caucus for the importance of commercial spaceflight in improving the cost and reliability of access to space. The best evidence for this is the recent joint House and Senate hearing on commercial human spaceflight, where I was invited to testify.
— Elon
[Note: SpaceX is always looking for truly exceptional engineers and offers a $3,000 bonus for any referrals that are hired. If you know someone that may fit the bill, please encourage them to send in their resume per instructions at www.spacex.com/careers.php.]
Propulsion
We fired the Falcon upper stage engine (Kestrel) for the first time in late July and, after some initially disappointing results, obtained solid combustion efficiency of almost 95%. Our target of 96% and a vacuum specific impulse of 325s should be achievable with a modification to the combustion chamber geometry. It gets exponentially more difficult to achieve each additional point of efficiency, so this is harder than it sounds.
This test is really a major milestone for SpaceX and places us within sight of achieving our design targets for both the main engine and the upper stage engine.
For those unfamiliar with the term, specific impulse is a benchmark for the overall efficiency of a rocket engine. The other critical term is the mass efficiency of the rocket stage as a whole, which tells you how much of the total is propellant vs. inert mass. Higher is better in each case.
As a basis for comparison, Boeing’s workhorse Delta II rocket upper stage has a specific impulse of 319s and a mass efficiency of 86%, compared to the expected Falcon specific impulse of 325s and mass efficiency of 91%. Our inert mass being one third better than Boeing’s is very significant as that translates to a pound for pound improvement in actual payload to orbit.
The biggest single advantage we have is our use of advanced aluminum-lithium for the propellant tanks rather than steel in the Boeing case. We also employ a blended system of both heated helium and gaseous oxygen to pressurize the tanks, significantly reducing our pressurant weight.
Avionics & Systems
Parachute Recovery of the First Stage
Our parachute recovery system from Irvin is nearing completion. The aluminum housing for the parachute and the 10,000lb mortar, as well as the drogue and main parachutes have been built. What remains is for the parachutes to be compressed and packed into the dispenser. For our part, we need to construct the recovery system attachment assembly within the interstage, put it all together, add the software triggers to our first stage computer and then the whole system will be complete.
The mortar is designed to be strong enough to fire the drogue chute out through the interstage at any attitude, even directly into the air flow, and still fully deploy. As a result, there is quite a hefty attachment ring at the base of the interstage. However, we plan on using the same ring for supporting the rocket against high ground winds by clamping it to the launch tower.
Thrust Vector Control Testing
We now have the thrust vector control stand fully set up for testing of the main engine and have done basic low pressure runs. Over the next several weeks, the thrust vector control system will be run through an exhaustive battery of tests to verify accuracy and speed, as well as iron out any anomalies.
Structures and Launch Operations
Launch Simulation
Below is an accelerated, low resolution launch simulation from the SpaceX complex at Vandenberg Air Force Base. The mobile rocket carrier also serves to support the launch tower against high wind conditions and contains the quick disconnect propellant supply lines.
Shortly before launch, the first stage pressurizes and the tower falls away, automatically disconnecting the propellant and electrical lines and pulling them under protective cover. Falcon is now in fully automatic mode and the only control to stop the launch resides with Air Force range safety.
The Merlin main engine turbo-pump spins up to over 20,000 rpm and the chamber ignites, achieving full thrust in less than a second. Falcon is held down by the launch supports while it runs internal diagnostics on Merlin to verify that everything looks good and then fires the hold down bolts for release to flight. Any out of the ordinary conditions will cause the flight computer to safely shut down the engine — another good reason to have liquid rocket engines rather than solid boosters!
Vertical Test Stand
Most of the structural work on the vertical stand at our propulsion test facility in Texas is complete. We will mount the full first stage of Falcon in this stand, attach the main engine (including thrust chamber, turbo-pump and thrust vector control) and begin full duration firings in late October or early November. Almost all systems, structures, electronics, software, etc on the first stage will be flight articles at that point. This is referred to as a stage hold-down test and is as near to an actual flight as the first stage will experience before the day of launch.