Chandrayaan-3 completes fourth engine burn in Earth orbit
According to India’s space agency ISRO, engineers have successfully completed the fourth of about six engine burns designed to raise Chandrayaan-3’s Earth orbit in preparation for sending it on its path to the Moon.
As shown in the graphic to the right, these adjustments are relatively small, but each increases the speed of the spacecraft at its orbit’s closest point to the Earth. That extra velocity thus reduces the amount of fuel needed for that trans-lunar-injection burn.
If all the maneuvers continue to go as planned, the landing attempt will occur around August 23, 2023.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
According to India’s space agency ISRO, engineers have successfully completed the fourth of about six engine burns designed to raise Chandrayaan-3’s Earth orbit in preparation for sending it on its path to the Moon.
As shown in the graphic to the right, these adjustments are relatively small, but each increases the speed of the spacecraft at its orbit’s closest point to the Earth. That extra velocity thus reduces the amount of fuel needed for that trans-lunar-injection burn.
If all the maneuvers continue to go as planned, the landing attempt will occur around August 23, 2023.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
Interesting choice by the Indian engineers. They chose the probability of a failure during one of of the multiple engine burns to a smaller payload with a fewer number of burns. They really trust the reliability of the. Rocket engine and the rest of the components of the space ship.
“ each increases the speed of the spacecraft at its orbit’s closest point to the Earth. ”
Is that due to the spacecraft being dragged along by the earth’s motion around the sun?
Bob Wilson: Nothing to do with the Earth’s orbit around the sun.
By simply raising the apogee (or high point), the speed as the spacecraft passes through the perigee (the low point) is simply faster. The spacecraft is falling farther toward the Earth, and thus picks up more velocity.
“ By simply raising the apogee (or high point), the speed as the spacecraft passes through the perigee (the low point) is simply faster. ”
They have to use fuel to raise the apogee. How does raising the apogee save fuel over directly using it to get to the moon?
Bob Wilson: I am no engineer, but I suspect this method requires a smaller engine with less thrust, saving overall weight. You do multiple small burns with this smaller engine, raise the speed, and then a smaller burn can get you to the Moon.
I am only guessing. Any real engineers out there to clarify?
https://en.wikipedia.org/wiki/Oberth_effect
To quickly summarize: by “falling” closer to the Earth, the speed of the spacecraft and the fuel onboard increases, adding kinetic energy to the system. Using the engine at this higher speed means that less propellant is needed, because the engine does not have to speed up the propellant that would have been needed to get to the speed at perigee. The planet has done some of the work for the spacecraft’s engine.
When the engine is a small one, several passes at perigee may be needed, because the shorter the burn, the more efficient the effect. If a long burn would have been needed, it becomes more efficient to break it up into a few shorter burns.
Edward said;
“by “falling” closer to the Earth, the speed of the spacecraft and the fuel onboard increases,”
With increase in speed by thrust, the spacecraft gets “further” from the earth and the effect a Gravity slingshot around the earth becomes less effective.
The short burn “isn’t” to “increase the speed of the craft” so much as it “redirects the craft back closer to the earth” where the gravity is stronger. As Edward pointed out, A closer flyby tosses the satellite further from the earth without nearly as much fuel consumed in a continuous burn.
A child on a swing performs a similar maneuver with their legs at the bottom of the arc. A low energy timed extension of the legs propels the swing higher and higher with each pass.
Here is what Wikipedia says about the maneuver. It does indeed use the motion of the Earth to give additional speed to the probe. They seem to use the maneuver in reverse to slow the spacecraft down when it gets around the moon.
“A gravity assist, gravity assist maneuver, swing-by, or generally a gravitational slingshot in orbital mechanics, is a type of spaceflight flyby which makes use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft, typically to save propellant and reduce expense.
Gravity assistance can be used to accelerate a spacecraft, that is, to increase or decrease its speed or redirect its path. The “assist” is provided by the motion of the gravitating body as it pulls on the spacecraft.[1] Any gain or loss of kinetic energy and linear momentum by a passing spacecraft is correspondingly lost or gained by the gravitational body, in accordance with Newton’s Third Law. The gravity assist maneuver was first used in 1959 when the Soviet probe Luna 3 photographed the far side of Earth’s Moon and it was used by interplanetary probes from Mariner 10 onward, including the two Voyager probes’ notable flybys of Jupiter and Saturn.“
https://en.m.wikipedia.org/wiki/Gravity_assist
Max is correct, that the lower the perigee the better the efficiency obtained by the Oberth effect. However, the spacecraft is not using its thrusters to lower the perigee, just to increase its apogee. Once in lunar orbit, it will use its thrusters to lower its apogee until it is able to land on the Moon.
Bob Wilson is also correct that the Oberth effect may be used for the gravity assist maneuver, but this is also not what is going on. These engine burns are raising the apogee. They do not use gravity to alter the path or speed of the spacecraft. Without the engine burns, the path would remain the same.
One could argue that once the Moon’s gravity becomes dominant and the spacecraft maneuvers into its orbit that the Moon’s gravity is used to change the spacecraft’s path. Because it will be. I wouldn’t have called that gravity assist, as I think of that maneuver more for changing course and speed toward another destination, rather than going into orbit around the body used for the gravity assist. In the case mentioned of the Mariner 10 and two Voyager spacecraft, gravity assist was used in the traditional slingshot maneuver to increase speed and direction to intersect with planets that are farther out from the Sun. In the case of Luna 3, the path was changed, similar to Apollo’s free-return trajectory, to return the spacecraft toward the Earth:
https://en.m.wikipedia.org/wiki/Luna_3#First_gravity_assist
Some probes have used Venus and Earth for slingshot maneuvers, but Parker and BepiColumbo used Venus in order to get closer to the Sun in a reverse of the slingshot maneuver but still using gravity assist and maybe the Oberth effect. I’m unsure about the latter; if they do not ignite the engine or use thrusters at or near the pericythe, then it does not use the Oberth effect.
https://en.m.wikipedia.org/wiki/Apsis#Terminology_summary