SPICE Kernels¶

Load a SPICE kernel into the global registry.

Known kernel names are downloaded from NAIF and cached: the planetary (DE) ephemerides "de430", "de432s", "de435", "de438", "de440", "de440s", "de442", "de442s"; the satellite ephemeris kernels "mar099", "mar099s", "jup365", "sat441", "ura184", "nep097", "plu060"; and the binary PCK "moon_pa_de440". Any other argument is treated as a local file path. SPK (.bsp) and binary PCK (.bpc) kernels are detected automatically from the file header. Loading is idempotent; kernels stay resident until unloaded, and later loads take precedence for overlapping coverage.

Parameters:

Raises:

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import brahe as bh

bh.load_spice_kernel("de440s")
print(bh.loaded_spice_kernels())

Unload a SPICE kernel from the global registry.

Parameters:

Raises:

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import brahe as bh

bh.load_spice_kernel("de440s")
bh.unload_spice_kernel("de440s")

Remove all kernels from the global registry.

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import brahe as bh

bh.clear_spice_kernels()
assert bh.loaded_spice_kernels() == []

List the kernels currently loaded in the global registry, in load order.

Returns:

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import brahe as bh

bh.load_common_spice_kernels()
assert "de440s" in bh.loaded_spice_kernels()

Load the kernels most applications need: "de440s" (planetary ephemeris) and "moon_pa_de440" (lunar principal-axes orientation).

~46 MB total on first download; cached thereafter. Each kernel load is idempotent, so calling this alongside other load_spice_kernel calls is safe.

Loading is not atomic: on error, kernels already loaded before the failure remain resident, so the call can be safely retried.

Raises:

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import brahe as bh

bh.load_common_spice_kernels()
print(bh.loaded_spice_kernels())

Load every kernel brahe knows how to download: "de440s", "moon_pa_de440", and the satellite ephemeris kernels "mar099s", "jup365", "sat441", "ura184", "nep097", "plu060".

~2.5 GB total on first download; cached thereafter. Prefer load_common_spice_kernels unless outer-planet body centers or moons are needed.

Loading is not atomic: on error, kernels already loaded before the failure remain resident, so the call can be safely retried.

Raises:

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import brahe as bh

bh.load_all_spice_kernels()
print(bh.loaded_spice_kernels())

Position of a target body relative to a center body from loaded SPK kernels.

The result is expressed in the kernel's inertial frame (ICRF axes; NAIF labels this "J2000"). If no kernels are loaded, DE440s is loaded automatically.

Parameters:

Returns:

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import brahe as bh

epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
r = bh.spk_position(bh.NAIFId.MOON, bh.NAIFId.EARTH, epc)

Velocity of a target body relative to a center body from loaded SPK kernels.

The result is expressed in the kernel's inertial frame (ICRF axes; NAIF labels this "J2000"). If no kernels are loaded, DE440s is loaded automatically.

Parameters:

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import brahe as bh

epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
v = bh.spk_velocity(bh.NAIFId.MOON, bh.NAIFId.EARTH, epc)

State (position and velocity) of a target body relative to a center body from loaded SPK kernels.

The result is expressed in the kernel's inertial frame (ICRF axes; NAIF labels this "J2000"). Computing the state shares a single record lookup between position and velocity. If no kernels are loaded, DE440s is loaded automatically.

Parameters:

Returns:

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import brahe as bh

epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
x = bh.spk_state(bh.NAIFId.SUN, bh.NAIFId.EARTH, epc)

Acceleration of a target body relative to a center body from loaded SPK kernels.

The result is expressed in the kernel's inertial frame (ICRF axes), evaluated by analytically differentiating the kernel's Chebyshev polynomials (twice for Type 2 segments; once, of the stored velocity polynomials, for Type 3). If no kernels are loaded, DE440s is loaded automatically.

Parameters:

Returns:

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import brahe as bh

epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
a = bh.spk_acceleration(bh.NAIFId.MOON, bh.NAIFId.EARTH, epc)

Position of a target body relative to a center body, queried from a single named kernel.

Queries that kernel only — no cross-kernel chaining is performed and the registry's last-loaded-wins precedence semantics do not apply. The kernel is auto-loaded by name or path if not already loaded.

Parameters:

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import brahe as bh

epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
r = bh.spk_position_from_kernel("de440s", bh.NAIFId.MOON, bh.NAIFId.EARTH, epc)

Velocity of a target body relative to a center body, queried from a single named kernel.

Queries that kernel only — no cross-kernel chaining is performed and the registry's last-loaded-wins precedence semantics do not apply. The kernel is auto-loaded by name or path if not already loaded.

Parameters:

Returns:

Raises:

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import brahe as bh

epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
v = bh.spk_velocity_from_kernel("de440s", bh.NAIFId.MOON, bh.NAIFId.EARTH, epc)

State (position and velocity) of a target body relative to a center body, queried from a single named kernel.

Queries that kernel only — no cross-kernel chaining is performed and the registry's last-loaded-wins precedence semantics do not apply. The kernel is auto-loaded by name or path if not already loaded.

Parameters:

Returns:

Raises:

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import brahe as bh

epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
x = bh.spk_state_from_kernel("de440s", bh.NAIFId.SUN, bh.NAIFId.EARTH, epc)

Acceleration of a target body relative to a center body, queried from a single named kernel.

Queries that kernel only — no cross-kernel chaining is performed and the registry's last-loaded-wins precedence semantics do not apply. The kernel is auto-loaded by name or path if not already loaded.

Parameters:

Returns:

Raises:

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import brahe as bh

epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
a = bh.spk_acceleration_from_kernel("de440s", bh.NAIFId.MOON, bh.NAIFId.EARTH, epc)

3-1-3 Euler angles and rates of a PCK body-fixed frame relative to ICRF.

PCKs are never auto-initialized; a PCK kernel must be explicitly loaded via bh.load_spice_kernel(...) first.

Parameters:

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import brahe as bh

bh.load_spice_kernel("moon_pa_de440")
epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
angles, rates = bh.pck_euler_angles(31008, epc)

3-1-3 Euler angle of a PCK body-fixed frame relative to ICRF.

PCKs are never auto-initialized; a PCK kernel must be explicitly loaded via bh.load_spice_kernel(...) first.

Parameters:

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import brahe as bh

bh.load_spice_kernel("moon_pa_de440")
epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
e = bh.pck_euler_angle(31008, epc)

Time derivatives of the 3-1-3 Euler angles of a PCK body-fixed frame.

PCKs are never auto-initialized; a PCK kernel must be explicitly loaded via bh.load_spice_kernel(...) first.

Parameters:

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Raises:

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import brahe as bh

bh.load_spice_kernel("moon_pa_de440")
epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
rates = bh.pck_euler_rates(31008, epc)

Typed Euler angle and its rates for a PCK body-fixed frame, from a single shared segment lookup.

PCKs are never auto-initialized; a PCK kernel must be explicitly loaded via bh.load_spice_kernel(...) first.

Parameters:

Returns:

Raises:

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import brahe as bh

bh.load_spice_kernel("moon_pa_de440")
epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
angle, rates = bh.pck_euler_angle_and_rates(31008, epc)

Orientation of a PCK body-fixed frame relative to ICRF, as a unit quaternion.

PCKs are never auto-initialized; a PCK kernel must be explicitly loaded via bh.load_spice_kernel(...) first.

Parameters:

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import brahe as bh

bh.load_spice_kernel("moon_pa_de440")
epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
q = bh.pck_quaternion(31008, epc)

Rotation matrix from ICRF to a PCK body-fixed frame.

PCKs are never auto-initialized; a PCK kernel must be explicitly loaded via bh.load_spice_kernel(...) first.

Parameters:

Returns:

Raises:

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import brahe as bh

bh.load_spice_kernel("moon_pa_de440")
epc = bh.Epoch.from_date(2025, 1, 1, bh.TimeSystem.UTC)
R = bh.pck_rotation_matrix(31008, epc)