TL;DR: For a Starship-class stack (~5,000 t at liftoff), “launch assistance” adding just 80–150 m/s early on can yield +5–13% payload to LEO depending on location. Moving the same vehicle to near-equatorial African highlands and combining with the best spring solution adds ~20 t to LEO and saves tens of tons of propellant on GEO missions by avoiding plane change. Every bit counts—and very much so.

0) Assumptions (to make the number reproducible)

• Vehicle mass at liftoff: 5,000,000 kg (Starship + Super Heavy class).
• Stage performance model (approximate but consistent):
  • First stage (booster): Isp ≈ 330 s, propellant ≈ 3,300 t, “dry” ≈ 200 t.
  • Second stage (ship): Isp ≈ 375 s, propellant ≈ 1,200 t, “dry” ≈ 150 t.
• Δv budget from pad to LEO (including gravity/drag losses): ~9.4 km/s.
• Earth's rotation: velocity addition at the equator vs. Starbase (~26° N latitude) ≈ +47 m/s.
• Equatorial GEO circularization plane change advantage (at apogee, combined maneuver): ≈ 305 m/s saved compared to 26° N latitude.
• Highland altitude advantage (thinner air, less drag) as an early Δv equivalent: ~10–20 m/s (we use 20 m/s in examples).

1) Three scenarios

Why not just a stadium-sized steel spring? Because steel's elastic energy density is low. The best practical "springs" are modules: electromagnetic sections, hydraulics, flywheels/SMES, and high-deformation composite cables—charged slowly, discharged quickly, force shaped by control.

2) Δv balance (what do we get "for free"?)

• Maglev lift: ~+80 m/s early.
• The big spring: ~+150 m/s early (world-class engineering and retention).
• Equator bonus vs. Starbase (~26°N): +47 m/s (spin).
• Highlands: ~+10–20 m/s Δv equivalent due to thinner air/pressure drop during the "dirtiest" seconds.
• GEO from the equator: saves ~305 m/s at apogee by avoiding 26° plane change.

3) How much useful payload does it "buy"? (LEO/SSO)

Using the sequential two-stage model described above, we get the following. The numbers are approximate; the pattern is important.

Read like this: the same rocket, with a small early push and a better pad, "charges" a double-digit ton number into LEO. This is the opposite of "small stuff."

4) Design "common sense" checks (stroke, force, energy)

• Stroke (v²/2a):
  • 80 m/s at +1 g → ~320 m.
  • 150 m/s at +2 g → ~563 m; at +3 g → ~375 m.
• Average force (M·Δv / t):
  • 80 m/s over 4 s → ~100 MN.
  • 150 m/s over 4 s → ~188 MN.
• Energy (½ M v²):
  • 80 m/s → 16 GJ (~4.4 MWh).
  • 150 m/s → 56 GJ (~15.6 MWh).

  Grid energy is simple; the hard part is power for a few seconds. That's why there is a "spring package": we charge slowly, release quickly, and build force.

5) GEO — where the equator amazes

From ~26°N (Starbase) to GEO flight you must "remove" ~26° inclination. If you do plane change smartly at apogee and combine it with circularization, the extra cost is ~305 m/s compared to launch from the equator.

What does 305 m/s mean in terms of propellant? For the second stage with Isp ≈ 375 s:

• Every 200 t after the maneuver (dry + payload) the apogee maneuver at the equator requires ~99 t of propellant, and the same from Starbase — ~125 t. That is a ~26 t saving—at apogee, for every mission.
• Scaling linearly: 400 t → ~52 t saved; 800 t → ~103 t saved.

Combine this with a 150 m/s spring push at liftoff and a highland launch site — and over the whole mission you add hundreds of m/s of "budget relief." In refueling architecture, this means fewer tanker flights or a larger payload to GEO.

6) Material reality check (why the "big" one isn’t magic yet)

• Today’s practical "spring packs" (steel/titanium + composites + EM engines): expected effective elastic energy density ~1–10+ kJ/kg. Enough for assistance, but not for "throwing into orbit."
• Laboratory "dream" variants (BMG, large deformation CFRP, someday CNT/graphene in mass) can achieve ~10–30+ kJ/kg practically. This allows ~150 m/s class assist at megastructure scale. Still, engines do the work.

7) Safety, control, and "don't break the rocket"

• Many small modules > one huge spring: redundant reliability and orderly aborts.
• S-curve limited by jerk: smooth force increase/hold/decrease; engines throttle together to keep total g within limits.
• Retention/dampers: all unused energy ends up in brakes, not in "bounce boostback."

8) The essence

• Maglev lift (~80 m/s): already worth ~+5 % LEO payload at Starbase, and even more at the equator.
• Big spring (~150 m/s): with world-class engineering, you get into the ~+9–13 % LEO payload range depending on location.
• Equatorial African Highlands + spring: about +20 t to LEO for the same rocket and ~25–100+ t propellant savings at GEO apogee (depending on the mission). This is the "every bit counts" — obviously.
• Engines still do the work: the spring doesn't replace thrust; it erases the worst first seconds and "pays" for it with the payload.

The zero stage can be a battery. Charge it slowly. Discharge it gently. With a better launch site and better latitude, you don't change physics — you let physics change your payload.