In article ,
says...

On 2018-03-12 20:37, Alain Fournier wrote:

Elon Musk said at South by Southwest that his Big Falcon Rocket
would start doing small test flights early next year.


"small test" ? a 1m high scale model with a tank of diet coke into which
a Mentos candy is dropped? :-)


Space-X apparently has begun to test its new Raptor engines.

For commercial aircraft, they can mount a new engine on a 747 and test
it in flight. (same fuel, and sufficiently spaced pylons make it
possible to mount new engine)


What are Musk's options to test fly the new engines?

BFS. It could be that the first BFS would be similar to Grasshopper or
Enterprise in that it won't have all the systems necessary for
supporting a crew in space. Automated testing only.

Can they built a Falcon-9 with a few raptor engines and a methane tank
instead of Kerosene for a test flight?

No, not without significant engineering, which would be a complete waste
of time and money.

Or must one assume that a test flight will be raptor engines on a BFR
stage 1 (even if it is topped by a cone instead of stage 2) ?

I believe BFS will be tested first. It has fewer engines than BFR.
Also, it might even have SSTO capability by itself without much payload
of course.

From a light load point of view, is it a problem of the methane and LOX
tanks are only partly fueled since this is such a short flight? or would
this require smaller tanks?

You can do a partial fill for short "hops". Does your car's gas tank
need to be full to make a trip to the grocery store?

Or can the tank be fitted with a helium
filled balloon that fill's the otherwise empty tank space?

WTF? Nope, nope, nope.

Jeff
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