Any Good Reason Not To Use Aerospike Rocketry If You Can Cancel Gravity and Also Possess Non-rocket Vacuum Only Scifi Propulsion?

[Spacescifi]

Scenario: A star wars like setting with SSTO vessels with hyperdrives being common.

Technology: All SSTOs possess gravity canceler tech, which allow vessels to float around as if in zero g despite gravity levels.

Space propulsion: A special vacuum seemingly reactionless drive is used for outer space only propulsion. In actuality it reacts with the vacuum itself...  a kind of vacuum propulsion akin to how air travel relies on the air itself.

Main Question: Obviously rocketry is still used to reach space, but due to gravity cancelation tech, SSTOs are far easier to make.

So the question now is... is there ANY legitimate reason NOT to use aerospike engines on SSTOs? Because I cannot think of one, and if I were an engineer in the setting I would propose slapping aerospike rockets onto every SSTO in the fleet I worked with.

Obviously star wars is not science accurate, and they use the same rocket engines for taking off planets that they use in space.... even though practically in real life this virtually is never optimal, efficient, or safe. Star Wars also never seems to utilize aerospikes either... with perhaps a few rare exceptions.

In the OP setting, special vacuum based non-rocket engines are used for outer space travel, which means you can afford to optimize your rocket engines purely for SSTO duty and RCS for steering in space.

So once again... any good reason to use a cluster of traditional bell nozzles over a singular big truncated aerospike surrounded by a ring of combustion chamber outlets?

Just to reach outer space? Since once there the vacuum space reaction engines take over for main thrust, and rocketry is only used for steering via the RCS.

[darthgently]

First thought: any tech that can cancel gravity for the ship overall combined with any tech than can generate internal gravity for crew would imply the ability to also use a variation of those techs to propel the craft.  The craft would "fall" in any direction one wanted.  So no justification of aerospikes other than to look cool. 

[Shpaget]

9 hours ago, Spacescifi said:

Star Wars also never seems to utilize aerospikes either

Air breathing engines have vastly superior ISP than rocket engines, so why not use some of that?

Turbofan/jet to get up to speed, then ram/scramjet to punch upwards out of the atmo, then your vacuum engine.

[darthgently]

4 hours ago, Shpaget said:

Air breathing engines have vastly superior ISP than rocket engines, so why not use some of that?

Turbofan/jet to get up to speed, then ram/scramjet to punch upwards out of the atmo, then your vacuum engine.

A single engine that origamistically™ reconfigures for each phase is the true sci-fi sol'n 

[Spacescifi]

5 hours ago, Shpaget said:

Air breathing engines have vastly superior ISP than rocket engines, so why not use some of that?

Turbofan/jet to get up to speed, then ram/scramjet to punch upwards out of the atmo, then your vacuum engine.

That won't work so well on planets like Mars with barely there atmosphere. Nor planets that don't have much oxygen (Saturn, Neptune, ect) unless you have an electrode jet, and those wear out with use.

Plasma jets are a thing but thrust is kinda weak compared to normal air jets.

To have something that will work anywhere you need rocketry.

[Terwin]

If you can ignore gravity and have a vacuum -only drive, why not just throw on a propeller?

Either the prop is enough to accelerate you or you can use your vacuum drive.  It can even be an electric prop so you only need fuel for the vacc drive.(You could throw it inside a shell for protection, but just making it retractable would likely be better)

[kerbiloid]

Tilt the repulsor, make the air flow back.

[Spacescifi]

4 hours ago, Terwin said:

If you can ignore gravity and have a vacuum -only drive, why not just throw on a propeller?

Either the prop is enough to accelerate you or you can use your vacuum drive.  It can even be an electric prop so you only need fuel for the vacc drive.(You could throw it inside a shell for protection, but just making it retractable would likely be better)

How about ductfans instead? They are more thrust efficient and make less noise.

In practice how an OP spaceship would enter an atmosphere from space:

1 . Slow speed to geostationary orbit while in low orbit using vacuum reaction engines and gravity cancellation in tandem. Because normally you would be falling in a curved trajectory as the atmosphere slows you. Here you slow in space without falling.

2. Toggle gravity cancellation field off. The result is you fall straight down... only long enough for you to reach an optimal velocity that you know your ductfans can counter to avoid crashing into the ground. In practice this also means traveling to a planet's surface will take longer, I don't know how long. Maybe an hour or two? Good news is you no longer have to worry about ablative heat tiles, because you never go fast enough in atmosphere to need them.

3. Leaving an atmosphere likewise will take longer than it would with rocketry. So do proper reconaissance before you decide to fly down to a planet, because if there is an enemy airforce chances are high you will be a BIG sitting duck to them.

 

4. I don't know if ductfans can do reverse thrust, but I think so, as I have seen turbofans on jet engines do it, and all turbofans are is a ducted fan with a jet engine in the middle. Ductfans rely on electric power, something a scifi spaceship will have plenty of usually by default. Gravity cancellation helps as well, but I would also presume that scifi spaceships can store larger amounts of electricity than modern batteries do.

Edited April 16 by Spacescifi

[darthgently]

But if you already can control gravity, using the same tech for propulsion is a no brainer.  As kerbiloid noted, merely cancel it off axis and you have gravity vectoring and you "fall" in the desired direction.

Adding fans or rocket engines would be like a motorcycle with vestigial bicycle pedals

[Nuke]

if you can cancel gravity you can get to orbit with a box fan. hell you could probably just flap your arms a lot (assuming your gravity canceler and its power supply fit in a backpack).

Edited April 19 by Nuke