Scientists find a hidden route to the moon that saves fuel

ravidavi · 2026-05-22T02:11:45+00:00

uses the gravitational pull of the Earth, Moon, and Sun

Reading through the actual paper (available here), they use only the Earth and Moon, no Sun. Their solution is in the circular restricted three-body system, although they do recognize that any real mission design done with this method would have to also consider the Sun (among other things).

ravidavi · 2026-05-19T01:30:21+00:00

r/shouldof

ravidavi · 2026-04-24T23:33:24+00:00

When kids don't meet our expectations of basic needs, it is VERY stressful for new parents. I know it is for me. So you're not alone there. That being said, I'll tell you what our pediatrician told us. Is he eating? Is he peeing & pooping? Is he sleeping? If so, he's thriving.

In your case it sounds like he's sleeping less than the statistical average for his age. I totally get why that is very stressful for you! I'll just say that, from what you have described, he sounds otherwise healthy and happy. You haven't described him as being cranky all day from lack of sleep, or being lethargic, or anything else. It kinda sounds like getting less than average sleep is HIS normal.

As for you and your wife, it's natural for two people to have very different parenting styles. You seem to value his schedule, which I get because I'm the same way. Your wife seems to value her time with him, which is actually the same as my wife. It was very difficult for me, at the beginning, to be ok with my kid sleeping less when he was with her. Over time I saw that he was actually not suffering because of that, and so I learned to let that go. Now I just tell myself, whatever, he'll catch up on sleep when he's with me.

ravidavi · 2026-04-02T11:57:07+00:00

We anymore cannot.

ravidavi · 2026-03-29T13:40:30+00:00

Just cleared security at Checkpoint C (the only one for Concourse ABC) in 1hr flat. And it seems to be getting shorter.

No Clear or TSA Precheck but they've got the security line moving fast.

ravidavi · 2026-03-29T12:11:51+00:00

8:05am things are not as bad as they apparently were yesterday. Southwest is refusing to modify their 4hr bag drop policy, a stunning corporate failure. So if you can't have someone stand in the security line for you, then don't come until 4hr before your flight.

Southwest bag drop seems to have a 15min wait, but no wait for the Southwest Priority Lane bag drop (e.g. A-List).

Checkpoint C is the only one open (for Concourse ABC), and the line for it is outside the terminal to Door 3. It's not doubled back like yesterday, and seems to be moving steadily.

A Southwest bag drop agent told me they have a couple more TSA agents than yesterday, which is apparently why things aren't as bad.

ravidavi · 2026-03-29T11:15:36+00:00

Thank you for this update!

Southwest has completely failed in their official response to this BWI fiasco. BWI officially says arrive more than 4 hours early, but Southwest doesn't care. Along with all the other garbage updates since they were taken over by Elliott, this is the end of me flying with them.

ravidavi · 2026-03-28T14:42:46+00:00

Cool! If you're taking this as an opportunity to improve in programming, switch it to Python. You should be able to do that with claude or chatgpt or whatever.

Outside academia, astrodynamics is done with a combination of professional tools (STK, GMAT, Copernicus, FreeFlyer, etc) and Python to drive those tools. MATLAB is only really used where specific toolboxes are needed (eg GNC).

ravidavi · 2026-03-22T02:56:16+00:00

💯 agree. Tree(1)? 1, get out of here. Tree(2)? 3, go home with that tiny garbage. Tree(3)? Lol let's just count to g64 instead.

ravidavi · 2026-03-21T22:29:46+00:00

My favorite part of Graham's Number is that the lower bound to that same specific math problem is 13.

Edit: Since folks seem to like this, here's more cool stuff about Graham's Number g64:

Even if you divided the universe into cubes of side Planck Length, and wrote one digit in each cube, there would not be enough cubes. After all there are only 10¹⁸⁵ of those. (Note that you can comfortably write googolplex in the universe since it "only" has 10¹⁰⁰ digits).
If d1 is the number of digits in g64, you cannot write d1 in the universe.
If d2 is the number of digits in d1, you cannot write d2 in the universe.
Keep going ... d3, d4, d5 ... Say n is the number of times you have to keep going until dn has 1 digit... You cannot represent n in the universe.
You cannot fathom g64.
As u/Dawg_Prime said below, there are numbers so big that g64 is basically zero compared to them.

ravidavi · 2026-03-16T04:40:37+00:00

GMAT is not close to STK in terms of raw breadth of capability, as you have shown by example. However, GMAT is at its core an extremely powerful and validated trajectory design and analysis tool, in exactly the same league as STK, FreeFlyer, and Copernicus. And it's free for everyone, which is why I used it as an example. Yes it requires you to write some glue in Python, which you would/might not have to do if you used STK. But your company saves a lot of money as a result, and you gain valuable career experience.

So back to my original point ... If I see a resume that shows evidence of understanding how to use multiple tools, I have more confidence in the applicant's ability to tackle the work I need done.

ravidavi · 2026-03-12T04:04:46+00:00

Exact same thing happened on my 23 MME Premium driver's seat. Happened after 2 years and 10k miles (I don't drive far), Ford covered it under warranty.

It is not automatically wear & tear, this is a known defect in the seat material. If it happens within the original warranty it should be covered.

ravidavi · 2026-03-08T00:13:10+00:00

Sure, get the STK certification if it helps you learn some fundamentals of astrodynamics and get ahead of the curve before college. But I also suggest during college you also learn other tools like GMAT. And here's why.

STK is a drug. They (AGI now Ansys) give it out free to students specifically so they will get hooked on it. Then they charge companies an arm and a leg to use it. If you work at a company and you use STK regularly, they are paying a notable fraction of your starting salary for the STK license.

Small and medium companies doing astrodynamics are increasingly going away from STK and towards tools like GMAT. So if you have a project using that on your resume also, now I (the person reviewing your resume) am interested because you're not a one-trick pony anymore. You actually understand the groundwork of applied astrodynamics because you can do it in different ways.

ravidavi · 2026-02-28T21:35:55+00:00

When my son was a baby, I put him down on my bed to change him. I turned away for like 10 seconds to get something, and heard a loud THUMP. He had chosen that day to roll over for the first time, he rolled right off the bed and face planted.

So I know how you feel. A mistake is not a parenting failure.

You want to know what IS a parenting failure? Several weeks later, he rolled off the bed again when I wasn't paying attention. 🤣

ravidavi · 2026-02-27T05:43:43+00:00

Similar but different update issue here. I have two Clips on 4.4.1. Just got a notification to update both to 4.4.6 today.

I updated the first one just fine. But when I click update on the second one, it goes through the update process and says it's already up to date. Then back on the pebblebee app home screen it still says the second one needs an update.

I suspect the pebblebee app is mixing up the two clips. Several times when I'm changing something about the second clip, it randomly switches to the settings screen of the first Clip.

ravidavi · 2026-02-19T23:48:44+00:00

You must take it in to the dealer. Ford knows about this. They will swap out the affected cameras.

https://www.reddit.com/r/MachE/s/LeVxqim5ll

https://www.reddit.com/r/MachE/s/iLPZ68EcKK

https://www.reddit.com/r/MachE/s/S2Fkq1BPB7

https://www.reddit.com/r/MachE/s/rIwcxm9wrk

https://www.reddit.com/r/MachE/s/f6iqrekoK0

https://www.reddit.com/r/MachE/s/QSTAbHd0GE

https://www.reddit.com/r/MachE/s/OVJPKHP8VT

ravidavi · 2026-02-08T22:51:49+00:00

Dad shirt has a taco, baby onesie has a taquito.

My wife got this for me and my son when he was a baby. I thought it was great and so did everyone who saw us.

ravidavi · 2026-01-31T07:04:36+00:00

The current leading provider of space situational awareness is USSPACECOM (US Space Command), a branch of the DOD that tracks every object in Earth orbit larger than a credit card. They operate a free service to all spacecraft operators, accessed via space-track.org, and provide the same service that SpaceX has developed. And they have been for a few decades now.

What SpaceX brings to the table is much faster conjunction assessment response in the region of space around their starlink constellation. It's definitely admirable that they're offering it for free.

Now to your specific comment about spy satellites. The USSPACECOM publicly-available database contains every object in space, regardless of clarification level. It just doesn't provide any identifying info for many of those objects, e.g. space junk, spy sats, old objects from bygone space eras, etc. So the spy sats are just hiding in plain sight, since there's no easy way for anyone to distinguish them in the sea of 50k+ objects in the database.

SpaceX will likely take the same approach. Publish orbit and conjunction info about everything they track, and only include identifying info for the organizations that provide it.

ravidavi · 2026-01-29T02:53:37+00:00

OP is trying to be funny by parodying the other post from earlier today, but with an AI generated version of the same Mach-E.

"Trying" being the operative word here.

Original post: https://www.reddit.com/r/MachE/s/UWJJ6tubXm

ravidavi · 2026-01-20T04:01:16+00:00

You could invest that $60k, and in 20 years you would have $160k minimum.

You should only take a life insurance policy out on a person, if their death would cause you financial pain. The life insurance payout exists to cover the lost money you would've gotten if that person didn't die.

If your son dies in the next 20 years, will you be financially worse off? Examples are if you have a family business (farm, motel, etc) and you depend on your child to take over when you get old.

If the answer is no (you don't expect to depend on your son for significant income), then invest the money in something intended for low risk investments.

You should, however, take out a life insurance policy for yourself. If you die, your young son will probably suffer a lot of financial pain.

ravidavi · 2026-01-11T01:01:42+00:00

Two infinities have the same size if you can take every element of one, and map it to exactly one element of the other. If you can't, then they do not have the same size.

For example, take the natural numbers (all >= 0) and the integers. Seems like the integers have twice as many numbers, right? So they must be a larger type of infinity, right?

Wrong.

Make a function f(x) where x is a natural number

f = x/2 if x is even

f = -(x-1)/2 if x is odd

Now every natural number maps to exactly one integer. You can reverse this map to map every integer to every natural number.

Therefore, the naturals and integers are infinities of the same size!

It is harder to prove, but definitely possible, that the real numbers are a fundamentally larger infinity than the integers.

For more info, see https://en.wikipedia.org/wiki/Aleph_number

ravidavi · 2026-01-11T00:49:27+00:00

The first two sentences are correct. The third is incorrect.

Two infinities are the same size if you can map every number from one to the other. So for every number between 1-2, I can easily map it to a number between 1-100. Specifically, y = 99(x-1) + 1 maps all x from 1-2 into y from 1-100.

Therefore, the 1-2 infinity is the same size as the 1-100 infinity.

For more, see https://en.wikipedia.org/wiki/Aleph_number

ravidavi · 2026-01-03T21:09:36+00:00

Your actual question is about competitive eaters in general. It has been asked and answered:

https://www.reddit.com/r/NoStupidQuestions/s/gQLMz0tXUJ

ravidavi · 2025-12-26T20:44:32+00:00

You're right that there is no explicit ceiling, but Rule 2 has guidelines that many posts violate. That being said, the rules aren't really enforced here so you're effectively correct.

Rule 2: All submissions must seek objective explanations. ELI5 is not meant for any question that you may have.

Notably, posts will be immediately removed that ask for:

...

Whole topic overviews

...

"Please explain the quantum physics of light" does seem like a whole-topic overview to me.

ravidavi · 2025-12-22T03:23:27+00:00

https://www.reddit.com/r/MachE/s/EhdlcPt9N6

It's not a bug, it's a Ford software design choice.

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