Spacecraft

Asset reference

Concept

In ASTROLAB a spacecraft is the central orbital actor of a mission study. It owns the dynamic state (orbit + attitude), participates in the 3D scene, and usually acts as the parent for payloads that see the Earth or talk to the ground: sensors, antennas, transmitters/receivers, solar arrays, and batteries.

Think of it as the digital twin of a satellite bus: mass and area properties feed drag/SRP and power; the propagator turns an initial state into an ephemeris over the scenario; attitude laws orient instruments and panels; constraints can further restrict when the spacecraft is allowed to “count” in access-like calculations.

Constellations do not replace spacecraft — a Walker or trailing constellation creates and groups member spacecraft that remain individually propagated.

Where in the UI

Action	How
Create	Mission Tree → Spacecraft category → Add Spacecraft (desktop context menu or mobile ⋯)
Edit	Select spacecraft → Properties (tabbed editor)
Apply	Apply Changes when the header shows dirty *
Children	Add from tree under the spacecraft, or manage Power/Battery panels inside the spacecraft tabs

Editor tabs

Tab	Purpose
Generic	Identity, mass properties, propagator
Orbit	State / frame / orbit design wizard / external ephemeris
Attitude	Attitude law and parameters
Visual	3D model, color, trail
COMM	Bus data-plane for Latency (MMFU, rates, processing)
Power	Bus size + solar array panels
Battery	Battery packs
Constraints	Access / environment constraints

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Generic

Parameter	Type	Default	Notes
Asset ID	text	—	Display / report name
Active in scene refresh	checkbox	—	When off, skipped on scene refresh
Mass [kg]	decimal	500	UI: Mass kg
Drag coefficient Cd	decimal	2.2
Geometric properties source	select	Constant Values / From Custom Assembly	Assembly needs a custom 3D design on the Visual tab
Area mode	select	Nominal / Randomly Tumbling / Max / Min	Only when From Custom Assembly
Drag area [m²]	decimal	1	Locked when areas come from the assembly
SRP coefficient Cr	decimal	1
Reflectivity area [m²]	decimal	1	Locked when areas come from the assembly
Propagator Type	select	Keplerian	See table below

Spacecraft Properties — Generic (mass, Cd, areas).

Propagator types

Apply Changes refreshes Design with the selected propagator (Keplerian, Eckstein–Hechler, DSST, or Numerical). Analyses that propagate the bus use the same choice.

Propagator	Description
Keplerian	Two-body analytical
Eckstein Hechler	Analytical (LEO-style perturbations)
DSST Propagator	Semi-analytical — efficient on long horizons
Numerical Propagator	Numerical integrator + force models (table below)

Numerical propagator options

Visible only when Propagator Type = Numerical Propagator:

Parameter	Type	Default
Min step [s]	decimal	0.001
Max step [s]	decimal	300
Abs tolerance	decimal	1e-6
Rel tolerance	decimal	1e-8
Gravity field Degree	integer	4
Gravity field Order	integer	4
Include atmospheric drag	checkbox	off
Atmosphere model	select	NRLMSISE-00 (also DTM2000, Harris-Priester, Simple Exponential)
Space weather source	select	CSSI Space Weather / Marshall Solar Activity Forecast / Constant Flux and GeoMag (web; F10.7, F10.7A, Kp). Desktop stores the same fields if the mission came from web.
Solar activity	select	Low / Moderate / High (Marshall only)
F10.7 / F10.7A / Kp	decimal	150 / 150 / 3 when space weather is Constant Flux
Include solar radiation pressure	checkbox	off
Include third-body point masses	checkbox	off. Web: when on, pick bodies (default Sun and Moon; also Mercury…Neptune). Desktop keeps the same on/off; a bodies list saved from web is preserved.

Spacecraft Properties — Generic (identity and propagator).

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Orbit

Parameter	Type	Options / notes
Epoch start UTC	text	Locked if external ephemeris is on
Epoch end UTC	text	Locked if external ephemeris is on
Coordinate frame	select	Inertial: EME2000, GCRF, TEME, TOD, MOD, CIRF, ECLIPTIC · Earth-fixed: ITRF
State type	select	Cartesian, Keplerian, Equinoctial, Delaunay — Keplerian/Equinoctial/Delaunay require an inertial frame (not ITRF)

State elements by type

State type	Parameters
Keplerian	SMA [km], ECC [-], INC [deg], RAAN [deg], AOP [deg], TA [deg]
Cartesian	X/Y/Z [km], VX/VY/VZ [km/s]
Equinoctial	a [km], ex, ey, hx, hy, Lv [deg]
Delaunay	L/G/H (×1e6), l/g/h [deg]

Orbit design wizard

Writes a designed orbit into the document when you click Design orbit (document) (Apply still required for the scene). Check that the initial state fields updated before applying.

Wizard class	Key parameters (min–max, default)
LEO Generic	alt_km 200–2000 (500), ecc 0–0.1 (0.001), inc_deg 0–180 (98.6), aop/raan/ta 0–360
LEO Alternative	perigee/apogee alt 200–2000, inc, aop/raan/ta
SSO	alt 400–900 (700), ecc, mltan_h 0–24 (10.5), aop/raan/ta
Repeating Ground-Track	revolutions 1–200 (14), cycle_days 1–100 (1), ecc, inc, raan, aop
SSO Repeating (I/D)	i 1–15 (3), d 2–20 (10), ecc, aop/raan/ta
GTO	perigee 200–2000 (250), apogee fixed ~35786 km, inc 0–90 (27)
GEO	alt fixed ~35786 km, ecc 0–0.01, inc 0–10
Molniya	perigee 500–1000 (600), apogee 39000–41000 (40000), inc ~63.4°, aop often 270°

External ephemeris

Parameter	Type	Notes
Use external ephemeris file	checkbox	Locks manual orbit editing
Load ephemeris file	file	.txt, .eph, .oem
Ephemeris file / external epoch	readonly	Filled after load

Orbit — frame and state vector.

Orbit — design wizard (SSO, LEO, GEO, …).

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Attitude

Parameter	Type	Options
Attitude law	select	Nadir, LVLH, QSW, TNW, VVLH, Inertial, Sun Pointing, Spin-Stabilized

Law	Extra parameters
Nadir	—
LVLH / QSW / TNW / VVLH	Roll/Pitch/Yaw [deg], Rotation order (XYZ…ZYX)
Inertial	Inertial frame (EME2000, GCRF, TEME, TOD, MOD, CIRF, ECLIPTIC)
Sun Pointing	Sun axis X/Y/Z (default Z = −1)
Spin-Stabilized	Base frame (Inertial/LOF), frame select, spin axis (±X/Y/Z), spin rate [deg/s]

Spacecraft Properties — Attitude (nadir and other laws).

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Visual

Parameter	Type	Default
Model	select	From resource catalog, or Point only
Color	color	#66E8FF typical
Model scale	decimal	Normalized Cesium scale
Trail [s]	decimal	3600
Show orbit path	checkbox	on
Show label in scene	checkbox	off

Spacecraft Properties — Visual (model, color, trail).

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COMM (spacecraft bus)

This tab is the data-plane size of the bus for Latency and ISL routing: how fast data is produced, how much can sit onboard, and how fast it can leave on a downlink or ISL. It is not the RF budget — EIRP, G/T, and margins live on Transmitter / Receiver and Link.

Each field is a value + unit pair.

How Latency uses the bus

Coverage answers when you acquire. Latency then moves bytes along a Connection Network. The spacecraft COMM fields are the caps on that move. Under ISL (CGR earliest delivery) they also size the ISL hop and how many radios may fire at once (CGR-ETO).

flowchart LR
  Cov["Coverage window"] --> Acq["Acquisition data rate"]
  Acq --> Mmfu["MMFU onboard"]
  Mmfu --> Isl["ISL Data Rate"]
  Mmfu --> Dl["Downlink Data Rate"]
  Isl --> Neigh["Neighbour MMFU"]
  Neigh --> Gnd["Facility"]
  Dl --> Gnd

The COMM tab groups the fields by link, each group with a one-line hint. The (i) button explains every parameter. Order: Onboard storage (MMFU) · Acquisition and processing · Downlink · ISL · Uplink from ground.

Field (editor)	Default	Where it is used
MMFU capacity	512 GB	Onboard mass memory. Acquired bytes accumulate here until a contact can drain them. If the tank fills, later data overflows (not delivered).
Acquisition Data Rate	150 Mbps	How fast this bus produces data while Coverage says it is acquiring — only if the acquirer is the spacecraft (no sensor, or Coverage picked the bus). Bytes ≈ rate × time. If Coverage’s acquirer is a sensor, Latency uses that sensor’s Acquisition data rate (default 80 Mbps) instead; the bytes still land in this spacecraft’s MMFU. Discrete Acquirer rate × acquisition window uses the same rule. Discrete Fixed payload size ignores this rate and uses the size you set on Latency.
Downlink Data Rate	450 Mbps	Space → ground hop. The hop is limited by the slower of this rate and the facility’s Max. RX Data Rate. Used on Direct dump and as the last hop after ISL.
ISL Data Rate	200 Mbps	Spacecraft → spacecraft hop when Latency (or Coverage command) policy is ISL (CGR earliest delivery). Pair rate = min of the two buses. Unused on Direct downlink.
Processing Latency	0 s	Store-and-forward delay added when a file arrives on this bus (ISL relay, or a Static IoT uplink) before it can be forwarded. Data the bus acquires itself does not pay it. CGR counts it when choosing the route, so a slow relay can lose to a later direct pass.
Max. Concurrent Downlink Links	1	How many X-band dumps may originate at this bus at once. Independent of the ISL radio: a satellite can dump to ground and forward ISL in the same step.
Max. Concurrent ISL Links	1	Parallel ISL transmits. When the Connection Network uses laser/antenna sensors, this count is per terminal (+V and −V can radiate together). When the CN rows are the buses, it is the spacecraft total. CGR-ETO and Session share that rule. X-band dump is the other knob.
Uplink Data Rate	2 Mbps	How fast the bus can receive from the ground. Static Latency: the uplink of each IoT packet and the session capacity of each user. Station command uplinks (Discrete facility tasking) also use it. It is not the downlink dump rate.
Max. Concurrent Uplinks	1	Static Latency only. How many ground clients (IoT sites or Session users) this bus receives at once. Continuous and Discrete ignore it, so a spacecraft with two sensors acquiring is never limited by it. Independent of ISL and X-band radios.

Sensor vs bus: production rate comes from the Coverage acquirer. Memory, uplink, space-to-ground and ISL always come from the parent spacecraft COMM tab. In Static, a site seen only by a sensor uplinks to that sensor's bus.

Three radio classes, not one: Max. Concurrent Uplinks receives from ground clients (Static only). Max. Concurrent ISL Links and Max. Concurrent Downlink Links are the relay and dump transmitters. Raising the uplink cap does not add parallel dumps.

Facility COMM is the other half of a downlink: Max. RX Data Rate, plus concurrent RX / processing — Facility.

After you change these numbers, re-run Latency (it goes stale). Changing COMM does not by itself recompute Coverage geometry or Link RF. Full picture: When analyses become stale.

Spacecraft Properties — COMM (MMFU, rates, ISL, concurrent radios).

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Power (solar arrays)

Solar arrays are child assets (solar_array) edited inside this tab (no standalone web editor).

Control	Meaning
Add panel / Remove panel	Create/remove solar_array children
Model source	Custom Design (bus X/Y/Z [m]) or Default Models
Per panel	Asset ID, Mount face (±X/Y/Z), Pos X/Y/Z [m], Euler sequence, R1/R2/R3 [°], Dim X/Y/Z [m], Use SADM, Pointing (Fixed / Sun-Tracking), SADM axis, Area [m²] (default 5), Efficiency (default 0.3)

Plan limit

solarArrayPerParent caps how many panels you can add per spacecraft.

Power — bus size and model source.

Power — solar-array panel card.

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Battery

Batteries are child assets (battery) edited in this tab.

Group	Parameters
Generic	Battery ID; Battery Type preset (Generic Li-Ion / LiFePO4 / NiH2) — applies chemistry defaults
Energy	Nominal Capacity [Wh] (default 500), Initial / Min / Max SOC [%]
Charge/discharge	Charge/Discharge efficiency [%], Max charge/discharge power [W]
Electrical bus	Nominal / Min / Max voltage [V]
Advanced	Self-discharge [%/day], Capacity degradation [%/yr], Min/Max operating temp [°C]

Validation: non-empty ID; capacity > 0; 0 ≤ min SOC ≤ max SOC ≤ 100; initial SOC in 0–100; nominal voltage > 0.

Plan limit

batteryPerParent caps batteries per spacecraft.

Spacecraft Properties — Battery (packs and SOC limits).

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Constraints

Constraint type	Default parameters
Range	min_km 0, max_km 2000
Ground elevation	min_deg 10, max_deg 90
Eclipse state	not_in / in
Target illuminated	(flag only)
Ground sun zenith angle	min_deg 0, max_deg 80
Altitude	min_km 0, max_km 2000
Solar beta angle	min_deg -90, max_deg 90

Each constraint card has Enabled and Remove.

Spacecraft Properties — Constraints (type, Enabled, parameters).

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Allowed children

Child type	How
sensor, antenna, transmitter, receiver	Tree → Add under spacecraft
solar_array, battery	Power / Battery tabs (preferred on web)

Example workflow

1. Add Spacecraft, set Asset ID SAT-DEMO.
2. Orbit wizard → SSO, altitude 700 km → Design orbit (document) → check that the initial state fields updated.
3. Attitude → Nadir.
4. Power → Add one sun-tracking panel.
5. Battery → Add Generic Li-Ion, 500 Wh.
6. Apply Changes (updates the 3D scene).
7. Optionally attach a sensor, then create Coverage / Power analyses.

Related

• Constellation · Sensors · Facility · Solar array · Battery
• Latency · ISL routing · Flight dynamics — Orbit · Independent verification · Mounted assets