There are several big risks. It's impossible to rank them in a credible way. Obviously there are all the usual launch risks. The cryogenics system has had a

There are several big risks. It's impossible to rank them in a credible way. Obviously there are all the usual launch risks. The cryogenics system has had a lot of development problems. The deployment is staggeringly complex and involves components that are not known for their robustness. Finally there is no repair option; one critical things goes wrong or is found to be misdesigned and that's it.