quote:

Originally posted by Georgeair:

quote:

Originally posted by trapper189:
At some point, the Moon's pull on the spacecraft will exceed
the Earth's pull and the spacecraft will start accelerating towards the Moon. I bet the math is interesting.

They've got a ways to go.... Turns out Earth is big.

The Earth-Moon L1 Lagrange point is located on the line connecting the Earth and the Moon, approximately 85% to 90% of the way to the Moon (about 320,000 to 340,000 km from Earth).

Livestream link

Since it has momentum towards the Moon, won't the spacecraft start accelerating towards the Moon well before L1? Also, the spacecraft will cross the line between the Earth and Moon, but won't travel on that line.

The crazier part is it really isn't going to accelerate towards the Moon, but rather an orbit of the Moon. It's also not slingshot like the wrist rocket slingshot, but rather the spacecraft is the shot in a David and Goliath type sling.

Like I said, I bet the math is interesting.

The math must be mind boggling for us mortals.
Imagine doing it in the 60's.

Is there any danger they could overshoot the moon and just keep going and not be able to return?

quote:

Originally posted by Georgeair:
The math must be mind boggling for us mortals.
Imagine doing it in the 60's.

Nerds with pocket protectors and slide rules.

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Originally posted by PASig:
Is there any danger they could overshoot the moon and just keep going and not be able to return?

They could overshoot if calculations are off, but I would hope they have enough fuel to use thrusters to come around and head back.
I don't think they would allow the ship to be that far off course, though.

quote:

Originally posted by trapper189:
Since it has momentum towards the Moon, won't the spacecraft start accelerating towards the Moon well before L1?

It will (did, now) begin accelerating when the TLI burn started. When the TLI burn ended, the force providing the acceleration ended. The spacecraft stopped accelerating and began coasting, always decelerating slightly due to Earth's gravity. Just like when your engine conks out while you're cruising down the freeway. After it reaches L1 it will start accelerating again due to the lunar gravity.

The change in the spacecraft's velocity will reach 0 well before L1. It has too. If the change in velocity reached 0 at L1, the spacecraft would be stuck there.

In other words, the only reason the spacecraft would be neither decelerating nor accelerating at L1 is if its velocity had reached 0 at that point as well.

I could be completely wrong though.

Never mind, I am completely wrong. The spacecraft's momentum will carry it through L1. It's like a Hot Wheels car on a straight track with a hill. If the car has just enough speed to get up the hill, then it will stop at the top of the hill. If it has more than enough, it will go past the top of the hill, but the change from deceleration to acceleration will always happen at the top of the hill.

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Originally posted by P250UA5:...

10 days total, with a 5k mile elevation flyby of the moon, which will make them the furthest ever traveled from Earth

Yes, and the moon is at its apogee putting it further from earth than it was during any of the manned Apollo missions.

Wonder if they NASA will play, Pink Floyd’s Dark Side of the Moon, for the crew.

You know there is no dark side of the moon, really.

quote:

Originally posted by trapper189:

Like I said, I bet the math is interesting.

I've been wondering what their navigational frame of reference is. There has to be some version of 0,0,0 on an xyz 3-dimensional grid for them to reference their position and velocity. Unlike terrestrial nav where we use lat/long.

If it were a simple 2D course that could be drawn on a flat piece of paper, the center of the Earth could suffice and the X-Y math wouldn't be too hard. But a 3D track?

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Originally posted by bcereuss:
You know there is no dark side of the moon, really.

But the Nazis have a base there.

How does the speedometer work?

Does it measure the change in the apparent diameter of the Moon over time?

Does it measure the change in the time radio signals from Earth get there and back?

Would either of those ideas even work since the spacecraft is not heading on a straight line path from the Earth to the Moon?

Is there universal background noise of which a change in pitch can be measured the faster you go, like a Doppler effect?

A question about the Apollo missions, for anyone in the know: After they landed on the moon and then took off again, how did the guys in the LEM find the command module to join back up? Sure, the moon isn't as big as the earth, but it's still pretty big and that's a big "sky" to find a little spacecraft in...

quote:

Originally posted by Gustofer:

quote:

Originally posted by Georgeair:
The math must be mind boggling for us mortals.
Imagine doing it in the 60's.

Nerds with pocket protectors and slide rules.

I wonder if they know how to use a slide rule. I imagine they have some scientific calculators for backup.

Right on track:

Artemis II Flight Day 3: Outbound Trajectory Correction Burn Update

NASA’s Artemis II crew in Orion continues on a precise trajectory to flyby the Moon on Monday, April 6. Flight controllers in mission control at NASA’s Johnson Space Center in Houston elected to cancel the spacecraft’s first outbound trajectory correction burn, as the spacecraft’s trajectory is on the right flight path.

This burn was the first of three planned trajectory adjustments in the mission timeline to fine‑tune the spacecraft’s velocity and trajectory. Any adjustments needed may be incorporated into a subsequent correction burn.

Appropriate that the mission named after the Ancient Greek goddess is heading for Selene, the Ancient Greek personification of the Moon.

quote:

Originally posted by trapper189:
How does the speedometer work?

IANAE (engineer), but out of curiosity I researched how to measure final speed based on acceleration over time. There's four values in the equation:

1. u = Initial Velocity
2. v = Final Velocity
3. a = Acceleration
4. t = Time

If three of the values are known, the unknown value can be determined. The formula for Final Speed is v = u + at.

I surmise there are Accelerometers in the crew module always measuring increase/decrease of G forces on a micro-scale. That, and a few computers to continually do the math, is probably what's being used to determine current speed. Subsequent navigational calculations that track the crew module trajectory and distance remaining should result in creating the correct intercept geometry to the moon.

That's my guess. Hopefully a real Rocket Scientist will drop in to correct my speculation.

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Originally posted by 92fstech:
A question about the Apollo missions, for anyone in the know: After they landed on the moon and then took off again, how did the guys in the LEM find the command module to join back up? Sure, the moon isn't as big as the earth, but it's still pretty big and that's a big "sky" to find a little spacecraft in...

Similar to sending the shuttle up to the space station - timing. Ground controllers know the orbit of the CM and simply (well, not quite that simple) time the launch of the LEM to meet up with the orbit of the CM.

I expect they have Inertial Reference Units on board. Aircraft have them to supplement or back up GPS. Prior to GPS they were standard on many airliners and corporate jets.

Iirc, the Space Shuttle had them. We built ring laser gyros for at least one military or space application many years ago in my first career.

Anyhow, some version of multi-axis accelerometers are used to calculate present position relative to a starting location. We used to have to initialize the IRS on the runway just prior to starting the takeoff roll. The IRS knew the precise lat/long of the runway we told it we were using. There was some drift in the calculated location vs reality over time, which would require an update after so many hours. Updating requires another method of fixing your position at a moment in time and then telling the IRS how much to correct. A spacecraft would have the same need to correct an IRU.

These days, terrestrial radar probably can determine a very precise location and speed of the spacecraft.

Apollo used star sightings and something similar to a sextant to figure their position enroute to/from the moon.

quote:

Originally posted by 92fstech:
A question about the Apollo missions, for anyone in the know: After they landed on the moon and then took off again, how did the guys in the LEM find the command module to join back up? Sure, the moon isn't as big as the earth, but it's still pretty big and that's a big "sky" to find a little spacecraft in...

Buzz Aldrin did his thesis on orbital rendesvous (IIRC they called him Dr Rendesvous). I believe this was a major part of the reason he was chosen for the first landing. If the computers and/or radar failed, he developed procedures for manual rendesvous and docking. You just can’t wing it.

Some stuff was done on the far side of the moon, during comms black-out. The accelleration burn, which would carry the spacecraft from lunar orbit to its trajectory home, was initiated without direct contact from Earth.