# Worked example — Kshana as the multi-tool mission-analysis glue layer
This walks one trajectory through the standards-based interop and mission-analysis
scenario kinds end-to-end, showing how Kshana sits *between* the high-fidelity tools
a programme already uses (GMAT, Orekit, STK for trajectory design; Basilisk/42 for
AOCS) rather than competing with them. Every step is a runnable scenario kind and
every output is **MODELLED** with its scope stated on the artifact.
> Honesty note: this is a *geometry/analytic* pipeline at the pre-Phase-A / trade-study
> tier. It is not a flight-dynamics certification — see each kind's `label` field.
## The pipeline
```
external FDS (GMAT/Orekit/STK) Kshana open core
│ CCSDS OEM ephemeris │
▼ ▼
[oem-interop] ──ingest──▶ [passes] ──▶ [link-budget] (when does the
import the orbit the when is it does the contact close?)
designer produced visible? downlink close?
│
▼
[space-weather] (how fast does drag
activity-driven decay the orbit?)
density
```
## 1. Ingest the trajectory a designer produced (`oem-interop`)
GMAT, Orekit and STK all *export* CCSDS Orbit Ephemeris Messages. Kshana imports
them — the other direction of the bridge — so a Kshana analysis can start from the
exact orbit the trajectory designer signed off, not a re-derived approximation:
```sh
kshana scenarios/oem-interop.toml # round-trips a reference orbit (self-test)
# or, to ingest a real file, set oem_text in the scenario to the external OEM
```
It reports the segments/objects/frames/epoch span and a velocity-consistency check,
proving the ephemeris was ingested faithfully (round-trip fidelity ~1e-7 km).
## 2. When is it visible from a ground station? (`passes`)
```sh
kshana scenarios/passes.toml
```
Predicts the rise/set passes (AOS / TCA / LOS, maximum elevation, duration) over a
station above an elevation mask, plus total access time — the ground-segment planning
query. (Keplerian propagation + Earth rotation; use an SGP4 propagator for
operational fidelity.)
## 3. Does the contact close? (`link-budget`)
For a pass, feed the slant range and the terminal figures into the CCSDS 401 /
DSN 810-005 link equation:
```sh
kshana scenarios/link-budget.toml
```
Reports free-space path loss, C/N₀, Eb/N₀, margin and whether the link **closes**
against a required Eb/N₀ — the comms feasibility check that turns "it's visible" into
"we can actually downlink the data."
## 4. How fast does the environment decay it? (`space-weather`)
```sh
kshana scenarios/space-weather.toml
```
Drives thermospheric neutral density from the solar (F10.7) and geomagnetic (Kp)
activity via the Jacchia-71 exospheric temperature — the ~5–10× solar-cycle density
swing the static atmosphere omits — so an orbit-lifetime / drag estimate reflects the
space-weather regime, not a fixed atmosphere.
## Why this is the glue, not a competitor
Each step is a small, auditable, reproducible scenario with an explicit honesty
label. The high-fidelity tools own trajectory optimisation, 6-DoF AOCS and aerothermal
EDL; Kshana owns the **open, citable, runnable connective tissue** — ingest the
standard formats, answer the cross-cutting geometry/feasibility questions, and hand
the result on — at a tier any partner can run without a licence. See also the
companion mission-analysis kinds `launch-window`, `reentry`, `eo-coverage`,
`space-packet` and `attitude-budget`.