ScenarioPosition half-way from Earth to the Moon

Genesis

New member
Hi Orbiters....I'm setting up a scenario where I wish to fly from Earth to the Moon...and I want to stop off at the FSS which I've installed as an add-on to refuel....but I want to place it half-way between Earth and the Moon but I have no idea what position to put in the scenario editor....any ideas on what figures to use please? ...thanks

Urwumpe

Not funny anymore
Donator
The problem is orbital mechanics there - simply half the distance between Earth and Moon would increase the amount of fuel you need in total and you would need to wait for a new window to continue the flight.

A much better place is the Earth-moon L1 lagrange point. It is closer to the moon, but requires only a small impulse to continue the flight in each direction.

Here you can find the approximate location, but much more precise is the Lagrange MFD:

Genesis

New member
HI Urwumpe, thank you for your reply....much appreciated....sounds a bit too complicated for me....LOL
What I've done is basically put it in an orbit around the earth (just copie an old Mir scenario and just changed the vessel from Mir to FSSB)....it's just something I would like to try....fly to the ISS...quick visit, then onto the FSS, refuel and then onto the Moon...think I was going a bit OTT placing it halfway...anyway, it's all fun!..thanks again

N_Molson

Donator
HI Urwumpe, thank you for your reply....much appreciated....sounds a bit too complicated for me....LOL
What I've done is basically put it in an orbit around the earth (just copie an old Mir scenario and just changed the vessel from Mir to FSSB)....it's just something I would like to try....fly to the ISS...quick visit, then onto the FSS, refuel and then onto the Moon...think I was going a bit OTT placing it halfway...anyway, it's all fun!..thanks again

Yes don't think in terms of distance but in terms of energy. That's what we call Delta-V, or differential of Velocity. Being in Low Earth Orbit is much more than doing "half the trip". You only need like 9,000 m/s of Delta-V to reach Earth Orbit (it includes aerodynamic drag losses) and from there like 3,200 m/s for Trans-Lunar Injection.

Urwumpe

Not funny anymore
Donator
Yes don't think in terms of distance but in terms of energy. That's what we call Delta-V, or differential of Velocity. Being in Low Earth Orbit is much more than doing "half the trip". You only need like 9,000 m/s of Delta-V to reach Earth Orbit (it includes aerodynamic drag losses) and from there like 3,200 m/s for Trans-Lunar Injection.

Most of the 9200 m/s total impulse is actually "losses" due to fighting against gravity. That factor is almost 1/4 of the total impulse, while aerodynamic losses are on the scale of about 300 m/s for a typical launch vehicle. (also that 9200 assumes you get the full rotation velocity of Earth by launching east)

Ajaja

Active member
Most of the 9200 m/s total impulse is actually "losses" due to fighting against gravity. That factor is almost 1/4 of the total impulse, while aerodynamic losses are on the scale of about 300 m/s for a typical launch vehicle. (also that 9200 assumes you get the full rotation velocity of Earth by launching east)
Somehow nobody ever counts wasted m/s due to rocket engine specific impulse losses in atmosphere.

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Urwumpe

Not funny anymore
Donator
Somehow nobody ever counts wasted m/s due to rocket engine specific impulse losses in atmosphere.

Its not that much, somewhere I had a ballpark number. Because it is so low, it never really made sense yet to use more advanced nozzles yet.

N_Molson

Donator
Yes, the dense part of the atmosphere is very thin. Pressure quickly drops with altitude and above 10 km it is marginal.

Ajaja

Active member
It's not so simple. You are forgetting about consequences of such ISP reduction.
Just go to https://launchercalculator.com/ and play with "1st stage Isp sea level or at the start altitude" changing it to the "1st stage Isp vacuum" value and watch "Gravity Losses" and "Aerodynamic Losses".
That's why I say that ISP losses because of the atmospheric pressure are worth than just "Aerodynamic Losses".

Urwumpe

Not funny anymore
Donator
It's not so simple. You are forgetting about consequences of such ISP reduction.
Just go to https://launchercalculator.com/ and play with "1st stage Isp sea level or at the start altitude" changing it to the "1st stage Isp vacuum" value and watch "Gravity Losses" and "Aerodynamic Losses".
That's why I say that ISP losses because of the atmospheric pressure are worth than just "Aerodynamic Losses".

Yeah, but that is an idealized rocket - how would it be like in reality?

Ajaja

Active member
Yeah, but that is an idealized rocket - how would it be like in reality?
It's about launching from planets with thick atmosphere or from planets/moons with thin atmosphere or without one. Aerodynamic drag it's not the only issue here.

I'm just reading Cold Eyes by Peter Cawdron and thinking about all these issues. It's a Sci-Fi novel about a high-G planet with thick atmosphere, shortage of heavy elements (so no nuclear fission energy) and how unlucky inhabitants of the planet stuck on its surface without any possibility to get to orbit using chemical rocket engines.

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Urwumpe

Not funny anymore
Donator
It's about launching from planets with thick atmosphere or from planets/moons with thin atmosphere or without one. Aerodynamic drag it's not the only issue here.

I'm just reading Cold Eyes by Peter Cawdron and thinking about all these issues. It's a Sci-Fi novel about a high-G planet with thick atmosphere, shortage of heavy elements (so no nuclear fission energy) and how unlucky inhabitants of the planet stuck on its surface without any possibility to get to orbit using chemical rocket engines.

And no, it isn't just about the planet, but also about the design of the rocket and its trajectory.

Ajaja

Active member
Yes, of course

And no, it isn't just about the planet, but also about the design of the rocket and its trajectory.
It's too. For example, engineers design nozzles for atmosphere and I wonder what limitations it adds to propellant ISP. Would it have much better ISP in vacuum with different nozzles (designed for vacuum) with the same propellant? And in general, how big a part plays atmosphere here and when it may become a bigger problem than gravity itself.

eddeford

New member
Hi Orbiters....I'm setting up a scenario where I wish to fly from Earth to the Moon...and I want to stop off at the FSS which I've installed as an add-on to refuel....but I want to place it half-way between Earth and the Moon but I have no idea what position to put in the scenario editor....any ideas on what figures to use please? ...thanks
Can I get a mars base scenario??

eddeford

New member
I han't done this for some time. What are the newest features?

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