Sundancer Orbital Trajectory Implications (Part Two)
In the first post in this series, I hinted at the idea that there may be a serendipitous benefit to Bigelow's choice of orbital inclination for Sundancer. I had received a refined version of the groundtrack trace, and it was subtly different from the first one, so I was trying to figure out exactly why it was different--just to make sure that I wasn't getting old data or had made some mistakes. I've received enough clarification to post this next section, but I'll probably have to wait another few days to finish things up, so bear with me--hopefully it will be more than worth the wait.
So, going back to the first part of this series, the main reasons driving the selection of the 41 degree repeating ground track orbit were: launch abort safety, providing a good view, and providing daily launch opportunities from Cape Canaveral (as well as daily landing opportunities at places like Edwards or White Sands). However, when I was looking at the US groundtrack map included in the Lockheed document, I noticed that Cape Canaveral wasn't the only existing or proposed US launch site that happens to be right under the ground track.
I don't have a good trajectory analysis software tool on hand, so I pinged a couple of friends that do, and over the past two weeks one of them helped me do some analysis of various launch sites across the world. We took the publically available information (with refinements from the info posted on L2 of NASASpaceFlight.com), and tried to back out from that a global groundtrack trace. The new data I have covers the groundtrack over the US, so while we try and figure out how to update our STK simulation to reflect the new info, I can at least comment on other US launch sites that could launch to or receive landings from Sundancer.
But with those caveats and disclaimers in place, let me dive into what we found.
Sundancer US Groundtrack
So here's the most up-to-date map of the US with the groundtrack for Sundancer superimposed:
As you can see, in addition to Cape Canaveral, several US launch and landing sites get at least daily launch and/or landing opportunities. Now, I'm not sure how far away from the groundtrack you can be and still reach it during a launch (ie I'm not sure how much extra delta-V that costs, and where the penalty gets so big that it's no longer worth it), but there are at least a few of those sites that are directly underneath the groundtrack shown:
- Wallops Island Launch Facility (located in Virginia) gets a launch opportunity every day on a descending track. Fortunately it looks like it is on an azimuth that Wallops can launch into. Wallops happens to have nearby communities and can only launch into a limited number of angles.
- White Sands, NM and the planned New Mexico Spaceport both have an opportunity once per day on a descending node.
- Nevada Test Site, NV also gets an opportunity once per day earlier on the same descending node. This was one of the proposed sites for Kistler's K-1 to launch out of. I'm not sure about the distances, but White Sands or New Mexico Spaceport might be far enough down range to allow the first stage to land there instead of committing a Return to Launch Site burn--this could increase payload substantially.
- Blue Origin's site near Van Horn, TX is also fairly close to that same descending ground track.
- The Chugwater, Wy facility that Frontier Astronautics is trying to get a launch site license for gets a daily launch and landing opportunity (at the peak of the orbital pass that gives Wallops its launch opportunity).
- Mojave Spaceport and Edwards Airforce Base are close enough for landing with a low cross-range vehicle (only need about 75-150 miles of cross range depending on which groundtrack pass you land off of), but I'm not certain if the delta-V penalty for a dogleg maneuver would preclude launching from there on the ascending pass that goes a bit to the south. If so, it might at some future point allow for a three-orbit mission that does a first orbit rendezvous, spends one orbit transfering crew and cargo, and then returns to its launch site the same day it leaves.
Void Where Prohibited, Your Mileage WILL Vary
Now, whether a given launch site can be used for this mission is going to depend a lot on subtle details of the planned trajectory, vehicle characteristics, operating modes, etc. An RLV can overfly inhabited portions of the country on its way to orbit so long as the "E-sub-c" number (the statistically predicted number of "Expected Casualties) per launch is low enough. This ends up being a combination of how densely populated the area under your groundtrack is, how fast your Instantaneous Impact Point is travelling when it passes over, and the probability of failure at that given point.
Obviously tweaking your trajectory to either avoid major population centers, or at least to have your IIP cross over them very quickly is preferred. For a vehicle like Sea Launch, even though they're using the unfortunately rather unreliable Zenit vehicle, they were able to get a launch license very easily for the specific reason that there's almost nothing for them to hit out there in the middle of the Pacific (well, alas, I may have to rephrase that as "nobody else" for them to hit...) It also helps if you're not intentionally dropping hardware every flight.
IIP is a calculation of where your vehicle would crash if its engines shut off and it went ballistic from that exact point in time. The interesting thing is that your IIP ends up travelling a lot faster than your vehicle itself, and in fact makes a complete loop around the earth on the way to orbit. There are subtle tricks that you can (and probably will have to) do in order to make sure that your IIP doesn't spend too much time crossing over a given population center.
Lastly, the odds of failure depend on both the proven reliability of the vehicle, and the riskiness of any given operation. At first, for a vehicle with no track record, the assumption is (for Ec calculations) is that you will crash your vehicle every single flight. However you're more likely to crash during certain risky maneuvers (such as staging, major throttle-ups/downs, Max-Q, etc). So you end up doing something that involves taking the total launch IIP trace for your vehicle, dividing it up into units of equal time, calculating the odds of it failing during each time window, adding dispersions, and figuring out what's the worst that can happen if it fails at that point. Or something like that. I can't say I know personally, as I've never had to experience that particular form of masochism.
Bottom line, if you want to launch from anywhere, you're going to be spending a lot of time with the AST. Make friends with them. Learn your stuff. They'll be right sometimes when you're wrong, and they'll be wrong some time when you're right. Humility mixed with boldness in correct ratios is in order. My gut feeling is that each of these launch sites, with the right amount of hard trajectory shaping, can be made to work. I'm sure that any AST guy/gal reading this is probably getting an ulcer by now, but I'm pretty sure they'd agree that there's probably a way to do it. Just budget a lot of time, and hire an ex-Marine if you can...
Further Thoughts on the Ramifications
Anyhow, assuming that some or most of these sites are feasible, I can think of a couple of near and medium-term ramifications:
- If SpaceX can get Falcon I flying reliably, and get Falcon IX built, they might be better off launching out of Wallops than Cape Canaveral. At Wallops they'd be one of the major players instead of being the poor stepchild. At Wallops they wouldn't be anywhere near as remote from civilization (and replacement parts or LOX shipments) as they are at Kwajelein. They could still launch into Sundancer's orbit, as well possibly as some polar orbits. This might eliminate entirely the need to launch from Vandenburg or Canaveral, and could end up saving them a lot of time, money, and hassle.
- As mentioned previously, if Rocketplane/Kistler ever get something flying, they also might be able to service Bigelow's station. They only get one daily pass, so they'd have a full day to rendezvous, dock, transfer crew/passengers/cargo/propellants, and then prepare for reentry. And as mentioned earlier, they could probably bump up their orbital payload by 20-50% or more by using a downrange landing site for their first stage, like White Sands, New Mexico Spaceport, or possibly Bezo's site.
- This trajectory while meeting near-term needs for Bigelow and Lockheed, also ends up being long-term beneficial to both them and new players. Bigelow wants cheaper launches. Lockheed and/or Boeing would love to operate orbital propellant depots and or tugs fueled by cheap alt.space RLVs. They aren't stupid. They're positioning themselves so that if a new low-cost provider comes into the field that they can find a way to profit from that too.
- Once Sundancer and eventually Nautilus are in orbit, and once they're being regularly serviced by capsule/ELV systems like Dragon/Falcon IX or Atlas V, it will provide a proven market at a destination that is conveniently reachable by emerging space startups from launch sites that have lower overhead and less bureaucracy (like several of the new commercial spaceports that are being proposed). This can possibly help start to break out of the chicken-and-egg problem we've been in for so long.
[Note: In the next post, once I've got a global groundtrack figured out, I'll comment on foreign/non-CONUS launch/landing sites that can access Sundancer. It may be a while, but preliminary info shows that at least Woomera and Kwaj look like they might be close. And the old unrefined data also showed the Japanese, Chinese, and Indians potentially winning as well. What will STK hold in store? Stay tuned...]
Labels: Launch Vehicles