1. The title that answers itself

Daniel Suarez’s Delta-V is a novel about asteroid mining where the title is both a plot device and a budget. Every manoeuvre costs delta-v, and once it is gone, the ship is stranded or dead. The desktop is not a mining ship, but its propellant budget is just as literal. This entry adds up what the desktop needs.

Entry 253 defined the propulsion attachment’s purpose. This entry estimates the delta-v budget.

2. Orbit and altitude assumptions

The desktop’s orbit was set in entry 189 as a low-inclination or sun-synchronous LEO, probably between 400 km and 600 km altitude. Drag is the dominant delta-v consumer at these altitudes. Higher orbits need less station-keeping but cost more to reach and have lower ground resolution for imaging.

For this budget, assume a 500 km circular orbit and a 5-year lifetime. This is a middle-of-the-road choice: drag is significant but manageable, and the view of Earth is useful.

3. Drag make-up

Atmospheric density at 500 km varies with solar activity by an order of magnitude. During solar maximum, drag can be several times higher than during solar minimum.

A rough estimate for a 100–150 kg desktop with a cross-sectional area of 1–2 m²:

  • Low solar activity: roughly 5–10 m/s per year.
  • Moderate solar activity: roughly 10–20 m/s per year.
  • High solar activity: roughly 20–40 m/s per year.

A conservative planning value is 20 m/s per year, giving 100 m/s over five years for drag make-up alone.

4. Collision avoidance

Conjunctions happen. A desktop that cannot move out of the way of debris is a liability. Each avoidance burn typically costs a few metres per second, though large uncertainties can drive it higher.

Assuming one to three conjunctions per year requiring manoeuvres:

  • Per burn: roughly 1–5 m/s.
  • Per year: roughly 5–10 m/s.
  • Over five years: roughly 25–50 m/s.

This is a statistical guess. The actual number depends on the traffic environment, the desktop’s orbit, and the operator’s risk tolerance.

5. Operational manoeuvres

The desktop may need to perform phasing, constellation management, or rendezvous with other objects. For a first desktop, these are secondary, but some capability should be budgeted.

  • Phasing within a few kilometres: roughly 1–5 m/s.
  • Small plane changes: tens of metres per second per degree, usually avoided.
  • Rendezvous with a keeper platform or servicer: roughly 10–50 m/s depending on geometry.

A conservative allowance for operational manoeuvres is 20–50 m/s over the lifetime.

6. Disposal

At end of life, the desktop must lower its perigee enough to re-enter within 25 years, as recommended by debris mitigation guidelines. From 500 km, this typically requires 50–100 m/s of delta-v, depending on the desired decay time and the area-to-mass ratio.

A reusable desktop might not dispose of itself immediately; it might move to a graveyard or parking orbit instead. But a first version should plan for controlled re-entry as the default.

7. Margin

Every budget needs margin for uncertainty, off-nominal burns, and propulsion system performance degradation. A reasonable margin is 20–30% on top of the calculated budget.

8. Total delta-v budget

Adding the items:

Item Delta-v
Drag make-up (5 years) 100 m/s
Collision avoidance 35 m/s
Operational manoeuvres 35 m/s
Disposal 75 m/s
Subtotal 245 m/s
Margin (25%) 60 m/s
Total 305 m/s

A rounded planning number is 300 m/s. This is enough for a 5-year mission at 500 km with conservative margins.

9. Translating delta-v to propellant mass

The propellant mass required depends on the rocket equation:

Δv = Isp · g₀ · ln(m₀ / m₁)

For a green monopropellant with Isp ≈ 220 s and a desktop dry mass of 120 kg:

  • Required mass ratio: exp(300 / (220 · 9.81)) ≈ 1.145.
  • Propellant mass: 120 · (1 − 1/1.145) ≈ 15 kg.

Add tank, feed system, and thruster mass, and the propulsion attachment grows to roughly 20–30 kg. This is comparable to the structural and power attachments.

What this changes

  • The desktop needs roughly 300 m/s of total delta-v for a 5-year mission at 500 km.
  • The largest items are drag make-up and end-of-life disposal.
  • Collision avoidance and operational manoeuvres add uncertainty but are smaller in total.
  • A 25% margin covers uncertainty and degradation.
  • A green monopropellant system needs roughly 15 kg of propellant for a 120 kg dry desktop.
  • The next entry can compare thruster technologies and choose a baseline.