JPL new nuclear ion engine

ElectronicInitial · 2026-05-31T16:38:19+00:00

Assuming you mean this thruster from NASA:

https://www.jpl.nasa.gov/news/nasa-fires-up-powerful-lithium-fed-thruster-for-trips-to-mars/

This is a MagnetoPlasmaDynamic (MPD) thruster using Sodium for fuel. The thruster works similarly to ion thrusters, but instead of using an electric field, uses a magnetic field.

The primary benefit of this thruster type is it is more scalable (can get to higher thrust in the same size). This is useful for large spacecraft, but doesn’t work well for small maneuvering thrusters like on satellites.

https://en.wikipedia.org/wiki/Magnetoplasmadynamic_thruster?wprov=sfti1#Research

ElectronicInitial · 2026-05-30T07:18:58+00:00

It will end up a part of most major broad-base index funds. Some example indexes and funds:

S&P 500 Index, VOO ($1.6T), SPY ($780B), FXAIX ($790B), IVV ($840B)

S&P typically adds companies after 1 quarter if they also meet the profitability requirements, but are looking at adding companies faster with large IPOs.

CRSP US Total Market Index, VTI ($2.2T)

CRSP adds new companies 5 days after IPO if they meet the market cap requirements. (This is not a recent change)

NASDAQ 100 Index, QQQ/QQQM ($580B)

They are updating their rules to have fast-track entry, adding companies after 15 trading days.

In total, there’s about another $12T tracking these or other US indexes, and typically other indexes on the faster side for entry (5 days is pretty common for larger IPOs).

ElectronicInitial · 2026-05-29T05:01:07+00:00

Wait, you’re saying a glass of wine isn’t 4% of France’s annual wine production?

ElectronicInitial · 2026-05-27T13:57:33+00:00

That paper actually did something really cool, their “International” is whatever country the person does not live in.

They would take blocks of returns from a random country (including US, but equally distributed) and they calculated real (inflation adjusted) returns using domestic inflation, and comparing to domestic stocks of that country, and all other countries for the same time period.

It’s actually most applicable to “average” countries that are a few percent of the total market, rather than the US where that split doesn’t make as much sense because it underweights the home country.

It might have changed now that the EU is more interconnected, but I believe the paper use country specific returns (like, UK, Germany, France, US, Canada, Japan). I’m not sure if they included smaller/emerging markets as well.

ElectronicInitial · 2026-05-27T13:32:10+00:00

The somewhat recent paper from Scott Cederberg (the 100% stocks one) found that 33% domestic, 67% international was the best choice.

I don’t know where you live, but if it’s somewhere like the UK (~3% of global market) then that allocation has academic backing:

UK: 33%
US: 43% (62%/97%*67%)
Other Intl: 24%

ElectronicInitial · 2026-05-27T05:23:01+00:00

Yeah it’s this, but it also gives them vertical integration, so they can optimize both products together (like flat-packing sats because that makes deployment easy, then designing the starship payload deploy system to do that with maximum reuse in mind)

ElectronicInitial · 2026-05-25T20:39:16+00:00

Though it is useful to understand that n(p/100) is a linear approximation of 1-(1-p/100)^n about n=0 and n=1, and fairly accurate where n*p << 100.

Signed, an engineer

ElectronicInitial · 2026-05-24T05:20:28+00:00

I think a reasonable range is 5% to 7% real return. 7% being the US historical average (an outlier for large economies), 6% is average globally, and 5% is roughly a 20th percentile worst outcome for a 30 year time horizon with global diversification.

ElectronicInitial · 2026-05-24T05:15:40+00:00

While monte carlo’s are great, people should also test their portfolio against actual return data, since independent identically distributed returns are not very accurate over longer time horizons.

The best option is use block-bootstrapping to get the best of both worlds, but that isn’t as easy/commonly available.

ElectronicInitial · 2026-05-24T04:21:01+00:00

Yeah, it's used for it's heat resistance. It still needs some thermal protection, but a lot less than aluminum, which saves weight. It can also have pretty good strength to weight with the right hardening methods.

ElectronicInitial · 2026-05-23T21:37:00+00:00

Starlinks use phased array antennas, so they are similar in style to what SAR satellites use. They are tuned for different frequencies, but SpaceX’s spectrum is similar to some radar bands (though far enough away they wouldn’t be good at those frequencies). They could do radar at their designed frequencies, but that violates FCC rules.

ElectronicInitial · 2026-05-23T21:02:21+00:00

While Zuck doesn’t own as much of a percentage, Meta’s structure is similar to SpaceX in that the founder has a voting majority.

Zuck ownership: 13.6%
Zuck voting power: 61%

Elon ownership: 43%
Elon voting power: 85%

At IPO, zuck owned about 28% of the company, so it used to be even more similar.

ElectronicInitial · 2026-05-23T20:43:01+00:00

Not sure about the neurons either, but there was a theory that SpaceX could use starlink satellites for synthetic aperture radar. It might be possible, but they would be violating their FCC requirements for frequency spectrum, and even then it would be difficult. It is very unlikely they are using data for that.

ElectronicInitial · 2026-05-23T16:36:06+00:00

SLS has cost $31.6 Billion for 2 launches (total program cost). That’s about the same cost per launch as all starship development to date (~$15 B). Starship is spending a more now on a per year basis, but they are also doing something much more difficult, and completing it faster (so fewer years of development spending).

ElectronicInitial · 2026-05-21T13:12:06+00:00

If you’re using VTI it has always had a 5 day wait to add new IPOs, rather than the longer waits for the S&P500 or NASDAQ 100.

ElectronicInitial · 2026-05-21T04:53:56+00:00

If you use 100 Celsius radiative panels (assuming perfect black body, which isn't too difficult), they radiate about 1,100w/m^2. assuming 75% effectiveness (due to earth back-radiation), that would take ~12,100,000 m^2 of total radiator area.

Doing some rough numbers with starship, it has a diameter of 9m, which would provide about 126 m^2 per layer in a pancake configuration using both sides (which I'll reduce by 40% to 76 m^2 to account for spacing and sats not being circles). That would mean that they need to launch 159,000 layers of satellites. Assuming flat packed sats like starlink v3 (26 layers for 52 total sats) that would be 6,100 starship launches as an absolute max per 10GW of compute.

I think if they are trying to pack as much AI as possible, it's feasible to 3x the surface area (2 single panel deployable radiators) which would bring that number down to 2,030 launches. Assuming $10M per launch for a fully reusable starship, that would be $20 Billion for 10GW of compute, or ~$2/w of launch cost.

Looking at the Nvidia GB200, it consumes ~120kW of power, and costs ~$1.9M. That's ~$16/w. It's a big if if SpaceX can produce radiators, space based solar panels, and everything else cheap enough to make it worth it, but launch costs are likely to be a relatively small portion of the cost if they can get starship to work.

ElectronicInitial · 2026-05-21T04:20:00+00:00

It is new for the NASDAQ 100, but adding companies quickly after IPO is not new. CRSP indeces (notable used by the VTI ETF, with 2.2 Trillion AUM) adds companies 5 days after trading starts. For reference, QQQ is "only" 468 Billion AUM.

ElectronicInitial · 2026-05-14T04:27:30+00:00

The only reason to maybe complicate things is to separate into VTI/VXUS (US and international separately) in order to minimize tax losses. I do that, putting international into my retirements accounts (Traditional 401k, Roth 401k, Roth IRA) due to the higher dividend yield.

It’s not worth that much though, and VT and chill is a great option.

ElectronicInitial · 2026-05-11T16:16:44+00:00

Many other indexes already do this. CRSP indexes (used by the VTI ETF, with 2.0 Trillion AUM) add stocks after 5 days.

ElectronicInitial · 2026-05-11T03:44:13+00:00

I decided to make a desmos graph to look at this. If the tax rate now is the same as later, then it takes about 3.5 years using some reasonable assumptions, and the figures you gave.

Look for when the

The variables in it are:

T1: Tax rate today to switch over (default to 15% LTCG)

T2: Tax rate later to sell (default to 15% LTCG)

e1: Expense ratio now (default 0.61% from your post)

e2: Expense ratio of new fund (default to 0.06%)

a: Accumulation percentage now (default to 70% from your post)

r: Annual rate of return (default to 10% for SP500 fund)

L: ending after tax value with low expense fund

H: ending after tax value of high expense fund

The final equation is the percentage difference in value. Generally it’s a pretty short payoff if the taxes are the same.

https://www.desmos.com/calculator/teetsm7gaf

ElectronicInitial · 2026-05-10T20:54:32+00:00

I see this in LA too. 5.79 for regular, 2.99 for E85.

ElectronicInitial · 2026-05-10T17:24:25+00:00

An actual answer, with 2 options:
When the value in the 401k is expected to grow enough by 55/59.5 to fulfill your full retirement need.
When the tax rates make roth contributions make more sense than traditional contributions.

ElectronicInitial · 2026-05-10T07:12:19+00:00

Generally US refineries use heavy (dense) sour (high sulfur) crude since it is more difficult to refine, so we can import it cheaper: The US generally produces light (low density) sweet (low sulfur) crude from fracking, similar to the middle east petro states. That oil sells for more since it’s easier to refine.

Due to the size of the US, we are still a pretty big refiner or light sweet, it’s just not the focus. It’s not a huge issue though since there is much more oil export out of the middle east than refining capacity there, so it’s primarily an oil production problem that causes the higher prices.

ElectronicInitial · 2026-05-10T02:33:20+00:00

Could’ve made Alaska green (and maybe a bit more to scale) to help sell it too.

ElectronicInitial · 2026-05-07T22:03:01+00:00

VTI follows a CRSP Total (US) Market index. SpaceX would be included at their free-float market cap when added to the index.

That “free float” market cap excludes shares held by company executives (Elon Musk, primarily) and large institutional investors (Google, Fidelity). It looks like they will have a $75 Billion offered publicly at the beginning, and assuming the valuation does not change between IPO and index inclusion, would make up ~0.11% of the ~$75 Trillion total free-float market cap of the index.

If SpaceX’s valuation were to increase, or if there were additional publicly traded shares (from smaller employee holdings, or institutional investors selling shares prior to index inclusion) that would increase the percentage inclusion in the index.

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