Some people get all the fun. You could charge admission to watch a test like this:
The secret payload traveled a distance of 3.61 miles in about six seconds on three sleds. Each sled ignited in stages to propel the cargo down the track. A helium tent enclosed nearly three miles of the 10-mile track in order to reduce the aerodynamic heating and drag on the payload.
Despite our earlier speculation, no one is saying what it was that traveled so fast. Navy sources did admit that, on top of the multiple sonic booms heard in the desert, the payload itself detonated at the end of the track.
I'll bet it did.
Let's play "Guess the mission"!
An offensive or a defensive weapon?
The nose cone emulates some ICBM RVs I've seen.
Defensive = shipboard abm test?
Offensive = GPS ICBM/IRBM warhead guidence?
Or possibly some ICBM reliability tests associated with arsenal mission assurance?
Let's play "Guess the mission"!
We don't have to. From the article ..
The electric system is meant to replace Navy warship's 5-in. guns.
Blow stuff up. Just a guess but this could be dual purpose and serve targets in both roles.
Two separate tests. One's obviously the railgun, they say as much. The other, they're not saying much. Interesting that they used a He "tent" to reduce drag for just about 5 or 6 km out of a 10-mile test track.
Most likely the "secret" test was something ICBM related, as pointed out the payload looks very much like an atmospheric reentry vehicle, and the use of the He tent indicates a desire to simulate exo-atmospheric conditions.
I did the math on the 7 lb slug with 10 megajoules of energy fired from the railgun. The muzzle velocity must be about 2500 m/s or about mach 7.3. This is pretty impressive and exceeds the maximum feasible projectile velocity for conventional explosive powered guns, so this will definitely be a step up if they are able to deploy it operationally. Also, in case anyone is wondering why it looks like the railgun slug is trailing a flaming exhaust plume, this is just friction heating of the air (much like the fireball on a reentry vehicle or meteor).
the use of the He tent indicates a desire to simulate exo-atmospheric conditions.
Exoatmospheric conditions involve helium at a pressure of 1 atmosphere?
No, the helium was likely there to reduce shock heating and drag by reducing the mach number and gas density.