Some supplies and equipment bound for the International Space Station were launched on Saturday. While this is typically a fairly routine process, this particular launch involved a SpaceX rocket that is meant to eventually be reusable. Rather than letting the initial stages of the rocket fall into the ocean, as is usually done, operators attempted to recover the first stage intact by landing it on a floating landing pad.
Unfortunately, it didn’t quite work, and the rocket landed a bit too hard and broke apart. The attempt was apparently quite close to working, which means that we may be close to a reusable launch system. That could be much cheaper than current methods where the rockets must be built anew for each launch. SpaceX officials claim that the chances of success were estimated to only be around 50-50, so the failure was not totally unexpected.
PRL published a couple new papers from AMS today, including this one, which shows an updated plot of the positron fraction (e+/(e+ + e-)) as a function of energy. I don’t think these have been posted to the arXiv yet, which is unusual for our field. Unfortunately, PRL must be accessed either through a network with access or with an account, which requires money, so if you’re not at a university and aren’t an APS member you might have trouble looking at the paper. In conjunction with the papers being released, there was a seminar at CERN earlier today. I didn’t find out about the seminar until it was too late for me to try to call in remotely.
AMS is a large multipurpose detector based at the International Space Station that studies cosmic rays, which are high energy particles flying around in space. The search for dark matter is one of the main purposes of the experiment, but it can study many things about cosmic rays, such as their composition, energy spectra, directions, etc.
This paper shows the positron fraction up to 500 GeV, which is a bit higher than in previous measurements. This measurement is useful for looking for dark matter annihilation to electron-positron pairs. The expected signal is for the positron fraction to increase at some energy and then peak and drop fairly sharply at an energy of approximately the dark matter mass. Previous measurements from AMS, Fermi, PAMELA and ATIC have all seen an increase in the ratio and have even seen the spectrum seem to level off. This new measurement shows that the leveling off continues, and the spectrum may even be starting to fall in the highest energy bin. However, the measurement is limited by both statistics and systematics at the highest energies, so the apparent decrease in the highest bin is not going to be statistically significant at this point in time. That may change with more events in the future and hopefully a better understanding of the detector and of astrophysical models for the non-dark matter background.
Earlier today, NASA announced the winners of contracts for developing spacecraft to send astronauts to the Interantional Space Station. Both Boeing and SpaceX have been awarded contracts, with Boeing receiving $4.2 billion and SpaceX getting $2.6 billion.
I would guess that Boeing received the most because it has a long track record of supplying equipment to the US government. NASA can safely assume that Boeing is capable of completing the contract. SpaceX hopes to be able to do spaceflight cheaper than anyone else but also hasn’t previously been involved in such a major undertaking. The contract shows that NASA is confident that SpaceX can do it, but they also won’t want to risk the whole program by awarding all the money to a company that hasn’t shown itself to be reliable.
Having two options is also a good idea so that a delay in one of them doesn’t necessarily delay the return of NASA-led manned launches. It might also turn out that the two vehicles are better at different things, so maybe some missions will favor Boeing and some SpaceX. Having some competition might also keep costs down.
NASA hopes to have the first launches in 2017, so we’ll still have a couple more years without having manned launch capabilities. Many had criticized the US government for ending the shuttle program because of this gap with no manned launch vehicle. The shuttle was a decades-old design that was very expensive and very risky for the crew, so I think that discontinuing shuttle launches was probably the right move. We should have already had a replacement vehicle ready, but not having one is not a sufficient justification to continue risking astronauts’ lives when safer but not US-led options were available.